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 $78.35   12.255%   $87.9518   $87.95   $87.95   $88.00  
  Purchase #2 $165.61   6.677%   $176.6678   $176.67   $176.65   $176.70  
  Purchase #3 $79.76   11.692%   $89.0855   $89.09   $89.10   $89.10  
  Purchase #4 $133.47   7.360%   $143.2934   $143.29   $143.30   $143.30  
  Purchase #5 $192.51   12.456%   $216.489   $216.49   $216.50   $216.50  
  Purchase #6 $176.92   10.732%   $195.9071   $195.91   $195.90   $195.90  
  Purchase #7 $7.54   5.492%   $7.9541   $7.95   $7.95   $8.00  
  7 purchase totals = $834.16       $917.3487   $917.35   $917.35   $917.50