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 $144.60   13.545%   $164.1861   $164.19   $164.20   $164.20  
  Purchase #2 $68.30   9.238%   $74.6096   $74.61   $74.60   $74.60  
  Purchase #3 $212.46   9.475%   $232.5906   $232.59   $232.60   $232.60  
  Purchase #4 $145.97   10.558%   $161.3815   $161.38   $161.40   $161.40  
  Purchase #5 $204.58   7.251%   $219.4141   $219.41   $219.40   $219.40  
  Purchase #6 $148.72   3.553%   $154.004   $154.00   $154.00   $154.00  
  Purchase #7 $225.40   8.429%   $244.399   $244.40   $244.40   $244.40  
  7 purchase totals = $1,150.03       $1,250.5849   $1,250.58   $1,250.60   $1,250.60