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 $87.98   6.438%   $93.6442   $93.64   $93.65   $93.60  
  Purchase #2 $132.58   11.402%   $147.6968   $147.70   $147.70   $147.70  
  Purchase #3 $206.50   10.159%   $227.4783   $227.48   $227.50   $227.50  
  Purchase #4 $59.31   12.534%   $66.7439   $66.74   $66.75   $66.70  
  Purchase #5 $38.30   6.809%   $40.9078   $40.91   $40.90   $40.90  
  Purchase #6 $148.66   3.363%   $153.6594   $153.66   $153.65   $153.70  
  Purchase #7 $77.38   11.383%   $86.1882   $86.19   $86.20   $86.20  
  7 purchase totals = $750.71       $816.3186   $816.32   $816.35   $816.30