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 $22.94   3.543%   $23.7528   $23.75   $23.75   $23.80  
  Purchase #2 $234.50   3.501%   $242.7098   $242.71   $242.70   $242.70  
  Purchase #3 $248.43   7.605%   $267.3231   $267.32   $267.30   $267.30  
  Purchase #4 $95.71   8.776%   $104.1095   $104.11   $104.10   $104.10  
  Purchase #5 $8.27   10.814%   $9.1643   $9.16   $9.15   $9.20  
  Purchase #6 $234.72   5.294%   $247.1461   $247.15   $247.15   $247.10  
  Purchase #7 $214.56   11.403%   $239.0263   $239.03   $239.05   $239.00  
  7 purchase totals = $1,059.13       $1,133.2319   $1,133.23   $1,133.20   $1,133.20