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 $213.48   13.626%   $242.5688   $242.57   $242.55   $242.60  
  Purchase #2 $174.94   4.233%   $182.3452   $182.35   $182.35   $182.30  
  Purchase #3 $34.28   6.540%   $36.5219   $36.52   $36.50   $36.50  
  Purchase #4 $32.43   13.370%   $36.7659   $36.77   $36.75   $36.80  
  Purchase #5 $230.71   8.505%   $250.3319   $250.33   $250.35   $250.30  
  Purchase #6 $30.30   6.429%   $32.248   $32.25   $32.25   $32.20  
  Purchase #7 $135.85   13.378%   $154.024   $154.02   $154.00   $154.00  
  7 purchase totals = $851.99       $934.8057   $934.81   $934.75   $934.70