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 $208.42   13.673%   $236.9173   $236.92   $236.90   $236.90  
  Purchase #2 $22.84   6.588%   $24.3447   $24.34   $24.35   $24.30  
  Purchase #3 $203.98   13.470%   $231.4561   $231.46   $231.45   $231.50  
  Purchase #4 $89.76   5.481%   $94.6797   $94.68   $94.70   $94.70  
  Purchase #5 $113.43   8.483%   $123.0523   $123.05   $123.05   $123.10  
  Purchase #6 $135.36   7.578%   $145.6176   $145.62   $145.60   $145.60  
  Purchase #7 $239.67   9.116%   $261.5183   $261.52   $261.50   $261.50  
  7 purchase totals = $1,013.46       $1,117.5860   $1,117.59   $1,117.55   $1,117.60