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 $148.79   12.766%   $167.7845   $167.78   $167.80   $167.80  
  Purchase #2 $64.39   6.197%   $68.3802   $68.38   $68.40   $68.40  
  Purchase #3 $89.61   4.562%   $93.698   $93.70   $93.70   $93.70  
  Purchase #4 $60.74   4.262%   $63.3287   $63.33   $63.35   $63.30  
  Purchase #5 $65.62   8.504%   $71.2003   $71.20   $71.20   $71.20  
  Purchase #6 $105.96   12.523%   $119.2294   $119.23   $119.25   $119.20  
  Purchase #7 $249.50   10.241%   $275.0513   $275.05   $275.05   $275.10  
  7 purchase totals = $784.61       $858.6724   $858.67   $858.75   $858.70