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 $183.91   11.871%   $205.742   $205.74   $205.75   $205.70  
  Purchase #2 $67.37   11.481%   $75.1047   $75.10   $75.10   $75.10  
  Purchase #3 $34.51   4.734%   $36.1437   $36.14   $36.15   $36.10  
  Purchase #4 $35.68   7.637%   $38.4049   $38.40   $38.40   $38.40  
  Purchase #5 $241.61   12.592%   $272.0335   $272.03   $272.05   $272.00  
  Purchase #6 $48.76   11.293%   $54.2665   $54.27   $54.25   $54.30  
  Purchase #7 $236.38   12.756%   $266.5326   $266.53   $266.55   $266.50  
  7 purchase totals = $848.22       $948.2279   $948.21   $948.25   $948.10