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 $206.77   3.633%   $214.282   $214.28   $214.30   $214.30  
  Purchase #2 $237.89   7.185%   $254.9824   $254.98   $255.00   $255.00  
  Purchase #3 $132.47   12.532%   $149.0711   $149.07   $149.05   $149.10  
  Purchase #4 $195.45   5.644%   $206.4812   $206.48   $206.50   $206.50  
  Purchase #5 $154.72   7.551%   $166.4029   $166.40   $166.40   $166.40  
  Purchase #6 $121.50   10.266%   $133.9732   $133.97   $133.95   $134.00  
  Purchase #7 $220.39   12.830%   $248.666   $248.67   $248.65   $248.70  
  7 purchase totals = $1,269.19       $1,373.8588   $1,373.85   $1,373.85   $1,374.00