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 $62.89   11.853%   $70.3444   $70.34   $70.35   $70.30  
  Purchase #2 $79.45   6.172%   $84.3537   $84.35   $84.35   $84.40  
  Purchase #3 $83.83   12.751%   $94.5192   $94.52   $94.50   $94.50  
  Purchase #4 $89.94   12.576%   $101.2509   $101.25   $101.25   $101.30  
  Purchase #5 $189.52   4.302%   $197.6732   $197.67   $197.65   $197.70  
  Purchase #6 $27.25   5.277%   $28.688   $28.69   $28.70   $28.70  
  Purchase #7 $244.46   12.105%   $274.0519   $274.05   $274.05   $274.10  
  7 purchase totals = $777.34       $850.8813   $850.87   $850.85   $851.00