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 $219.60   11.672%   $245.2317   $245.23   $245.25   $245.20  
  Purchase #2 $58.89   9.538%   $64.5069   $64.51   $64.50   $64.50  
  Purchase #3 $189.65   5.798%   $200.6459   $200.65   $200.65   $200.60  
  Purchase #4 $26.45   11.308%   $29.441   $29.44   $29.45   $29.40  
  Purchase #5 $187.82   11.628%   $209.6597   $209.66   $209.65   $209.70  
  Purchase #6 $161.97   4.596%   $169.4141   $169.41   $169.40   $169.40  
  Purchase #7 $79.33   6.780%   $84.7086   $84.71   $84.70   $84.70  
  7 purchase totals = $923.71       $1,003.6079   $1,003.61   $1,003.60   $1,003.50