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 $84.49   11.246%   $93.9917   $93.99   $94.00   $94.00  
  Purchase #2 $43.65   12.710%   $49.1979   $49.20   $49.20   $49.20  
  Purchase #3 $45.60   3.648%   $47.2635   $47.26   $47.25   $47.30  
  Purchase #4 $103.92   7.775%   $111.9998   $112.00   $112.00   $112.00  
  Purchase #5 $59.53   10.771%   $65.942   $65.94   $65.95   $65.90  
  Purchase #6 $158.69   3.378%   $164.0505   $164.05   $164.05   $164.10  
  Purchase #7 $120.69   5.482%   $127.3062   $127.31   $127.30   $127.30  
  7 purchase totals = $616.57       $659.7516   $659.75   $659.75   $659.80