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 $146.53   4.202%   $152.6872   $152.69   $152.70   $152.70  
  Purchase #2 $158.34   12.563%   $178.2323   $178.23   $178.25   $178.20  
  Purchase #3 $191.49   3.694%   $198.5636   $198.56   $198.55   $198.60  
  Purchase #4 $16.66   12.245%   $18.7   $18.70   $18.70   $18.70  
  Purchase #5 $120.79   11.419%   $134.583   $134.58   $134.60   $134.60  
  Purchase #6 $59.73   5.457%   $62.9895   $62.99   $63.00   $63.00  
  Purchase #7 $104.38   4.595%   $109.1763   $109.18   $109.20   $109.20  
  7 purchase totals = $797.92       $854.9319   $854.93   $855.00   $855.00