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 $232.73   12.788%   $262.4915   $262.49   $262.50   $262.50  
  Purchase #2 $149.75   11.832%   $167.4684   $167.47   $167.45   $167.50  
  Purchase #3 $119.58   8.793%   $130.0947   $130.09   $130.10   $130.10  
  Purchase #4 $66.25   12.592%   $74.5922   $74.59   $74.60   $74.60  
  Purchase #5 $62.81   5.580%   $66.3148   $66.31   $66.30   $66.30  
  Purchase #6 $164.72   8.586%   $178.8629   $178.86   $178.85   $178.90  
  Purchase #7 $148.86   8.601%   $161.6634   $161.66   $161.65   $161.70  
  7 purchase totals = $944.70       $1,041.4879   $1,041.47   $1,041.45   $1,041.60