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 $84.68   4.262%   $88.2891   $88.29   $88.30   $88.30  
  Purchase #2 $209.31   12.582%   $235.6454   $235.65   $235.65   $235.60  
  Purchase #3 $91.91   3.800%   $95.4026   $95.40   $95.40   $95.40  
  Purchase #4 $106.79   13.680%   $121.3989   $121.40   $121.40   $121.40  
  Purchase #5 $208.58   12.243%   $234.1164   $234.12   $234.10   $234.10  
  Purchase #6 $242.65   7.634%   $261.1739   $261.17   $261.15   $261.20  
  Purchase #7 $16.84   11.728%   $18.815   $18.82   $18.80   $18.80  
  7 purchase totals = $960.76       $1,054.8413   $1,054.85   $1,054.80   $1,054.80