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 $104.58   13.851%   $119.0654   $119.07   $119.05   $119.10  
  Purchase #2 $92.48   9.479%   $101.2462   $101.25   $101.25   $101.20  
  Purchase #3 $115.44   5.114%   $121.3436   $121.34   $121.35   $121.30  
  Purchase #4 $150.58   3.575%   $155.9632   $155.96   $155.95   $156.00  
  Purchase #5 $154.94   4.648%   $162.1416   $162.14   $162.15   $162.10  
  Purchase #6 $37.96   3.476%   $39.2795   $39.28   $39.30   $39.30  
  Purchase #7 $215.64   5.777%   $228.0975   $228.10   $228.10   $228.10  
  7 purchase totals = $871.62       $927.1370   $927.14   $927.15   $927.10