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 $228.98   7.843%   $246.9389   $246.94   $246.95   $246.90  
  Purchase #2 $212.28   7.127%   $227.4092   $227.41   $227.40   $227.40  
  Purchase #3 $157.46   7.662%   $169.5246   $169.52   $169.50   $169.50  
  Purchase #4 $49.28   4.652%   $51.5725   $51.57   $51.55   $51.60  
  Purchase #5 $160.47   10.728%   $177.6852   $177.69   $177.70   $177.70  
  Purchase #6 $213.93   5.320%   $225.3111   $225.31   $225.30   $225.30  
  Purchase #7 $180.78   9.793%   $198.4838   $198.48   $198.50   $198.50  
  7 purchase totals = $1,203.18       $1,296.9253   $1,296.92   $1,296.90   $1,296.90