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 $137.42   8.585%   $149.2175   $149.22   $149.20   $149.20  
  Purchase #2 $214.93   13.365%   $243.6554   $243.66   $243.65   $243.70  
  Purchase #3 $224.61   8.468%   $243.63   $243.63   $243.65   $243.60  
  Purchase #4 $151.56   10.109%   $166.8812   $166.88   $166.90   $166.90  
  Purchase #5 $182.60   7.260%   $195.8568   $195.86   $195.85   $195.90  
  Purchase #6 $203.26   4.806%   $213.0287   $213.03   $213.05   $213.00  
  Purchase #7 $230.57   3.579%   $238.8221   $238.82   $238.80   $238.80  
  7 purchase totals = $1,344.95       $1,451.0917   $1,451.10   $1,451.10   $1,451.10