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 $170.29   9.423%   $186.3364   $186.34   $186.35   $186.30  
  Purchase #2 $29.63   13.179%   $33.5349   $33.53   $33.55   $33.50  
  Purchase #3 $167.60   13.830%   $190.7791   $190.78   $190.80   $190.80  
  Purchase #4 $97.71   7.837%   $105.3675   $105.37   $105.35   $105.40  
  Purchase #5 $181.85   5.310%   $191.5062   $191.51   $191.50   $191.50  
  Purchase #6 $89.49   9.473%   $97.9674   $97.97   $97.95   $98.00  
  Purchase #7 $156.75   8.718%   $170.4155   $170.42   $170.40   $170.40  
  7 purchase totals = $893.32       $975.9070   $975.92   $975.90   $975.90