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 $236.67   10.598%   $261.7523   $261.75   $261.75   $261.80  
  Purchase #2 $115.44   3.401%   $119.3661   $119.37   $119.35   $119.40  
  Purchase #3 $22.25   11.527%   $24.8148   $24.81   $24.80   $24.80  
  Purchase #4 $199.58   3.548%   $206.6611   $206.66   $206.65   $206.70  
  Purchase #5 $138.95   12.240%   $155.9575   $155.96   $155.95   $156.00  
  Purchase #6 $112.51   5.347%   $118.5259   $118.53   $118.55   $118.50  
  Purchase #7 $181.95   11.431%   $202.7487   $202.75   $202.75   $202.70  
  7 purchase totals = $1,007.35       $1,089.8264   $1,089.83   $1,089.80   $1,089.90