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 $64.30   11.573%   $71.7414   $71.74   $71.75   $71.70  
  Purchase #2 $99.61   5.289%   $104.8784   $104.88   $104.90   $104.90  
  Purchase #3 $249.39   10.871%   $276.5012   $276.50   $276.50   $276.50  
  Purchase #4 $174.58   8.731%   $189.8226   $189.82   $189.80   $189.80  
  Purchase #5 $64.54   10.584%   $71.3709   $71.37   $71.35   $71.40  
  Purchase #6 $87.91   5.660%   $92.8857   $92.89   $92.90   $92.90  
  Purchase #7 $47.99   4.155%   $49.984   $49.98   $50.00   $50.00  
  7 purchase totals = $788.32       $857.1842   $857.18   $857.20   $857.20