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 $186.97   3.794%   $194.0636   $194.06   $194.05   $194.10  
  Purchase #2 $248.77   13.427%   $282.1723   $282.17   $282.15   $282.20  
  Purchase #3 $164.40   9.323%   $179.727   $179.73   $179.75   $179.70  
  Purchase #4 $32.93   11.861%   $36.8358   $36.84   $36.85   $36.80  
  Purchase #5 $158.45   11.681%   $176.9585   $176.96   $176.95   $177.00  
  Purchase #6 $133.85   11.814%   $149.663   $149.66   $149.65   $149.70  
  Purchase #7 $61.31   13.693%   $69.7052   $69.71   $69.70   $69.70  
  7 purchase totals = $986.68       $1,089.1254   $1,089.13   $1,089.10   $1,089.20