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 $121.54   3.134%   $125.3491   $125.35   $125.35   $125.30  
  Purchase #2 $69.42   13.698%   $78.9292   $78.93   $78.95   $78.90  
  Purchase #3 $62.37   3.351%   $64.46   $64.46   $64.45   $64.50  
  Purchase #4 $244.37   8.456%   $265.0339   $265.03   $265.05   $265.00  
  Purchase #5 $209.51   13.565%   $237.93   $237.93   $237.95   $237.90  
  Purchase #6 $166.30   10.575%   $183.8862   $183.89   $183.90   $183.90  
  Purchase #7 $172.87   4.295%   $180.2948   $180.29   $180.30   $180.30  
  7 purchase totals = $1,046.38       $1,135.8832   $1,135.88   $1,135.95   $1,135.80