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 $81.53   8.594%   $88.5367   $88.54   $88.55   $88.50  
  Purchase #2 $62.78   4.684%   $65.7206   $65.72   $65.70   $65.70  
  Purchase #3 $116.59   11.437%   $129.9244   $129.92   $129.90   $129.90  
  Purchase #4 $148.28   11.678%   $165.5961   $165.60   $165.60   $165.60  
  Purchase #5 $45.85   3.470%   $47.441   $47.44   $47.45   $47.40  
  Purchase #6 $111.62   12.741%   $125.8415   $125.84   $125.85   $125.80  
  Purchase #7 $107.65   8.683%   $116.9972   $117.00   $117.00   $117.00  
  7 purchase totals = $674.30       $740.0575   $740.06   $740.05   $739.90