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 $204.59   3.869%   $212.5056   $212.51   $212.50   $212.50  
  Purchase #2 $95.29   6.617%   $101.5953   $101.60   $101.60   $101.60  
  Purchase #3 $151.63   6.488%   $161.4678   $161.47   $161.45   $161.50  
  Purchase #4 $200.36   8.566%   $217.5228   $217.52   $217.50   $217.50  
  Purchase #5 $29.79   12.429%   $33.4926   $33.49   $33.50   $33.50  
  Purchase #6 $207.65   4.359%   $216.7015   $216.70   $216.70   $216.70  
  Purchase #7 $11.77   4.474%   $12.2966   $12.30   $12.30   $12.30  
  7 purchase totals = $901.08       $955.5822   $955.59   $955.55   $955.60