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 $112.61   4.809%   $118.0254   $118.03   $118.05   $118.00  
  Purchase #2 $120.74   8.473%   $130.9703   $130.97   $130.95   $131.00  
  Purchase #3 $37.30   4.211%   $38.8707   $38.87   $38.85   $38.90  
  Purchase #4 $87.49   4.763%   $91.6571   $91.66   $91.65   $91.70  
  Purchase #5 $116.77   3.447%   $120.7951   $120.80   $120.80   $120.80  
  Purchase #6 $204.27   7.418%   $219.4227   $219.42   $219.40   $219.40  
  Purchase #7 $30.92   5.194%   $32.526   $32.53   $32.55   $32.50  
  7 purchase totals = $710.10       $752.2673   $752.28   $752.25   $752.30