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 $85.35   12.855%   $96.3217   $96.32   $96.30   $96.30  
  Purchase #2 $44.79   9.485%   $49.0383   $49.04   $49.05   $49.00  
  Purchase #3 $153.25   12.564%   $172.5043   $172.50   $172.50   $172.50  
  Purchase #4 $30.40   5.670%   $32.1237   $32.12   $32.10   $32.10  
  Purchase #5 $46.72   7.301%   $50.131   $50.13   $50.15   $50.10  
  Purchase #6 $213.92   5.226%   $225.0995   $225.10   $225.10   $225.10  
  Purchase #7 $231.49   3.201%   $238.9   $238.90   $238.90   $238.90  
  7 purchase totals = $805.92       $864.1185   $864.11   $864.10   $864.00