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 $68.87   12.795%   $77.6819   $77.68   $77.70   $77.70  
  Purchase #2 $227.49   5.222%   $239.3695   $239.37   $239.35   $239.40  
  Purchase #3 $84.52   9.739%   $92.7514   $92.75   $92.75   $92.80  
  Purchase #4 $60.30   11.788%   $67.4082   $67.41   $67.40   $67.40  
  Purchase #5 $188.39   13.422%   $213.6757   $213.68   $213.70   $213.70  
  Purchase #6 $245.90   13.676%   $279.5293   $279.53   $279.55   $279.50  
  Purchase #7 $64.81   8.809%   $70.5191   $70.52   $70.50   $70.50  
  7 purchase totals = $940.28       $1,040.9351   $1,040.94   $1,040.95   $1,041.00