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 $70.83   6.634%   $75.5289   $75.53   $75.55   $75.50  
  Purchase #2 $71.99   12.412%   $80.9254   $80.93   $80.95   $80.90  
  Purchase #3 $235.32   6.601%   $250.8535   $250.85   $250.85   $250.90  
  Purchase #4 $166.69   5.309%   $175.5396   $175.54   $175.55   $175.50  
  Purchase #5 $102.34   5.685%   $108.158   $108.16   $108.15   $108.20  
  Purchase #6 $12.38   10.357%   $13.6622   $13.66   $13.65   $13.70  
  Purchase #7 $250.56   3.607%   $259.5977   $259.60   $259.60   $259.60  
  7 purchase totals = $910.11       $964.2653   $964.27   $964.30   $964.30