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 $58.39   6.107%   $61.9559   $61.96   $61.95   $62.00  
  Purchase #2 $148.36   5.544%   $156.5851   $156.59   $156.60   $156.60  
  Purchase #3 $119.63   8.198%   $129.4373   $129.44   $129.45   $129.40  
  Purchase #4 $114.70   11.387%   $127.7609   $127.76   $127.75   $127.80  
  Purchase #5 $174.89   11.115%   $194.329   $194.33   $194.35   $194.30  
  Purchase #6 $165.82   4.782%   $173.7495   $173.75   $173.75   $173.70  
  Purchase #7 $49.96   8.572%   $54.2426   $54.24   $54.25   $54.20  
  7 purchase totals = $831.75       $898.0603   $898.07   $898.10   $898.00