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 $114.33   10.354%   $126.1677   $126.17   $126.15   $126.20  
  Purchase #2 $190.54   12.762%   $214.8567   $214.86   $214.85   $214.90  
  Purchase #3 $78.58   5.390%   $82.8155   $82.82   $82.80   $82.80  
  Purchase #4 $85.87   3.464%   $88.8445   $88.84   $88.85   $88.80  
  Purchase #5 $62.86   6.109%   $66.7001   $66.70   $66.70   $66.70  
  Purchase #6 $23.43   10.756%   $25.9501   $25.95   $25.95   $26.00  
  Purchase #7 $165.73   3.223%   $171.0715   $171.07   $171.05   $171.10  
  7 purchase totals = $721.34       $776.4061   $776.41   $776.35   $776.50