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 $66.58   7.117%   $71.3185   $71.32   $71.30   $71.30  
  Purchase #2 $230.83   3.263%   $238.362   $238.36   $238.35   $238.40  
  Purchase #3 $151.84   7.593%   $163.3692   $163.37   $163.35   $163.40  
  Purchase #4 $87.93   8.596%   $95.4885   $95.49   $95.50   $95.50  
  Purchase #5 $216.51   11.690%   $241.82   $241.82   $241.80   $241.80  
  Purchase #6 $103.50   11.276%   $115.1707   $115.17   $115.15   $115.20  
  Purchase #7 $107.47   13.386%   $121.8559   $121.86   $121.85   $121.90  
  7 purchase totals = $964.66       $1,047.3848   $1,047.39   $1,047.30   $1,047.50