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 $110.88   11.224%   $123.3252   $123.33   $123.35   $123.30  
  Purchase #2 $92.50   6.269%   $98.2988   $98.30   $98.30   $98.30  
  Purchase #3 $221.60   11.480%   $247.0397   $247.04   $247.05   $247.00  
  Purchase #4 $26.66   6.151%   $28.2999   $28.30   $28.30   $28.30  
  Purchase #5 $80.98   4.673%   $84.7642   $84.76   $84.75   $84.80  
  Purchase #6 $177.95   11.364%   $198.1722   $198.17   $198.15   $198.20  
  Purchase #7 $69.98   4.782%   $73.3264   $73.33   $73.35   $73.30  
  7 purchase totals = $780.55       $853.2264   $853.23   $853.25   $853.20