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 $60.70   5.782%   $64.2097   $64.21   $64.20   $64.20  
  Purchase #2 $196.68   12.680%   $221.619   $221.62   $221.60   $221.60  
  Purchase #3 $116.34   4.282%   $121.3217   $121.32   $121.30   $121.30  
  Purchase #4 $211.48   9.730%   $232.057   $232.06   $232.05   $232.10  
  Purchase #5 $169.31   4.154%   $176.3431   $176.34   $176.35   $176.30  
  Purchase #6 $202.41   5.254%   $213.0446   $213.04   $213.05   $213.00  
  Purchase #7 $214.62   4.753%   $224.8209   $224.82   $224.80   $224.80  
  7 purchase totals = $1,171.54       $1,253.4160   $1,253.41   $1,253.35   $1,253.30