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 $184.28   12.613%   $207.5232   $207.52   $207.50   $207.50  
  Purchase #2 $70.67   3.176%   $72.9145   $72.91   $72.90   $72.90  
  Purchase #3 $43.93   11.281%   $48.8857   $48.89   $48.90   $48.90  
  Purchase #4 $197.63   9.637%   $216.6756   $216.68   $216.70   $216.70  
  Purchase #5 $103.68   4.468%   $108.3124   $108.31   $108.30   $108.30  
  Purchase #6 $246.49   8.480%   $267.3924   $267.39   $267.40   $267.40  
  Purchase #7 $28.62   12.800%   $32.2834   $32.28   $32.30   $32.30  
  7 purchase totals = $875.30       $953.9872   $953.98   $954.00   $954.00