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 $93.64   4.260%   $97.6291   $97.63   $97.65   $97.60  
  Purchase #2 $73.87   5.693%   $78.0754   $78.08   $78.10   $78.10  
  Purchase #3 $64.51   6.523%   $68.718   $68.72   $68.70   $68.70  
  Purchase #4 $121.37   4.779%   $127.1703   $127.17   $127.15   $127.20  
  Purchase #5 $187.54   12.776%   $211.5001   $211.50   $211.50   $211.50  
  Purchase #6 $159.49   3.529%   $165.1184   $165.12   $165.10   $165.10  
  Purchase #7 $58.70   13.619%   $66.6944   $66.69   $66.70   $66.70  
  7 purchase totals = $759.12       $814.9057   $814.91   $814.90   $814.90