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 $61.31   6.604%   $65.3589   $65.36   $65.35   $65.40  
  Purchase #2 $198.95   11.766%   $222.3585   $222.36   $222.35   $222.40  
  Purchase #3 $81.70   3.707%   $84.7286   $84.73   $84.75   $84.70  
  Purchase #4 $147.34   6.507%   $156.9274   $156.93   $156.95   $156.90  
  Purchase #5 $126.33   10.655%   $139.7905   $139.79   $139.80   $139.80  
  Purchase #6 $107.38   8.257%   $116.2464   $116.25   $116.25   $116.20  
  Purchase #7 $207.95   4.420%   $217.1414   $217.14   $217.15   $217.10  
  7 purchase totals = $930.96       $1,002.5517   $1,002.56   $1,002.60   $1,002.50