Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $144.34   5.344%   $152.0535   $152.05   $152.05   $152.10  
  Purchase #2 $229.83   13.707%   $261.3328   $261.33   $261.35   $261.30  
  Purchase #3 $121.55   6.641%   $129.6221   $129.62   $129.60   $129.60  
  Purchase #4 $211.39   9.748%   $231.9963   $232.00   $232.00   $232.00  
  Purchase #5 $166.96   11.121%   $185.5276   $185.53   $185.55   $185.50  
  Purchase #6 $183.81   5.388%   $193.7137   $193.71   $193.70   $193.70  
  Purchase #7 $204.83   5.145%   $215.3685   $215.37   $215.35   $215.40  
  7 purchase totals = $1,262.71       $1,369.6145   $1,369.61   $1,369.60   $1,369.60