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 $194.85   5.714%   $205.9837   $205.98   $206.00   $206.00  
  Purchase #2 $68.96   9.276%   $75.3567   $75.36   $75.35   $75.40  
  Purchase #3 $165.81   7.207%   $177.7599   $177.76   $177.75   $177.80  
  Purchase #4 $18.36   6.339%   $19.5238   $19.52   $19.50   $19.50  
  Purchase #5 $18.97   3.569%   $19.647   $19.65   $19.65   $19.60  
  Purchase #6 $194.57   8.444%   $210.9995   $211.00   $211.00   $211.00  
  Purchase #7 $236.60   3.172%   $244.105   $244.11   $244.10   $244.10  
  7 purchase totals = $898.12       $953.3756   $953.38   $953.35   $953.40