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 $241.97   8.411%   $262.3221   $262.32   $262.30   $262.30  
  Purchase #2 $88.70   9.232%   $96.8888   $96.89   $96.90   $96.90  
  Purchase #3 $83.43   12.456%   $93.822   $93.82   $93.80   $93.80  
  Purchase #4 $24.44   7.750%   $26.3341   $26.33   $26.35   $26.30  
  Purchase #5 $119.42   10.849%   $132.3759   $132.38   $132.40   $132.40  
  Purchase #6 $207.32   13.381%   $235.0615   $235.06   $235.05   $235.10  
  Purchase #7 $59.49   12.411%   $66.8733   $66.87   $66.85   $66.90  
  7 purchase totals = $824.77       $913.6777   $913.67   $913.65   $913.70