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 $56.66   12.509%   $63.7476   $63.75   $63.75   $63.70  
  Purchase #2 $189.25   3.525%   $195.9211   $195.92   $195.90   $195.90  
  Purchase #3 $108.26   5.148%   $113.8332   $113.83   $113.85   $113.80  
  Purchase #4 $168.98   4.147%   $175.9876   $175.99   $176.00   $176.00  
  Purchase #5 $65.40   4.390%   $68.2711   $68.27   $68.25   $68.30  
  Purchase #6 $79.53   11.485%   $88.664   $88.66   $88.65   $88.70  
  Purchase #7 $87.37   13.108%   $98.8225   $98.82   $98.80   $98.80  
  7 purchase totals = $755.45       $805.2471   $805.24   $805.20   $805.20