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 $153.75   8.197%   $166.3529   $166.35   $166.35   $166.40  
  Purchase #2 $235.56   11.195%   $261.9309   $261.93   $261.95   $261.90  
  Purchase #3 $204.96   13.632%   $232.9001   $232.90   $232.90   $232.90  
  Purchase #4 $194.98   8.526%   $211.604   $211.60   $211.60   $211.60  
  Purchase #5 $60.85   8.798%   $66.2036   $66.20   $66.20   $66.20  
  Purchase #6 $235.66   5.321%   $248.1995   $248.20   $248.20   $248.20  
  Purchase #7 $44.65   3.281%   $46.115   $46.12   $46.10   $46.10  
  7 purchase totals = $1,130.41       $1,233.3060   $1,233.30   $1,233.30   $1,233.30