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 $116.64   13.692%   $132.6103   $132.61   $132.60   $132.60  
  Purchase #2 $200.57   7.519%   $215.6509   $215.65   $215.65   $215.70  
  Purchase #3 $10.73   13.750%   $12.2054   $12.21   $12.20   $12.20  
  Purchase #4 $86.80   11.181%   $96.5051   $96.51   $96.50   $96.50  
  Purchase #5 $196.93   4.291%   $205.3803   $205.38   $205.40   $205.40  
  Purchase #6 $124.88   12.323%   $140.269   $140.27   $140.25   $140.30  
  Purchase #7 $159.41   7.495%   $171.3578   $171.36   $171.35   $171.40  
  7 purchase totals = $895.96       $973.9788   $973.99   $973.95   $974.10