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 $60.42   12.166%   $67.7707   $67.77   $67.75   $67.80  
  Purchase #2 $27.38   3.843%   $28.4322   $28.43   $28.45   $28.40  
  Purchase #3 $244.61   9.541%   $267.9482   $267.95   $267.95   $267.90  
  Purchase #4 $210.79   8.351%   $228.3931   $228.39   $228.40   $228.40  
  Purchase #5 $216.75   3.712%   $224.7958   $224.80   $224.80   $224.80  
  Purchase #6 $239.46   3.563%   $247.992   $247.99   $248.00   $248.00  
  Purchase #7 $231.25   4.679%   $242.0702   $242.07   $242.05   $242.10  
  7 purchase totals = $1,230.66       $1,307.4022   $1,307.40   $1,307.40   $1,307.40