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 $97.92   7.615%   $105.3766   $105.38   $105.40   $105.40  
  Purchase #2 $223.49   12.196%   $250.7468   $250.75   $250.75   $250.70  
  Purchase #3 $232.88   3.611%   $241.2893   $241.29   $241.30   $241.30  
  Purchase #4 $87.35   7.205%   $93.6436   $93.64   $93.65   $93.60  
  Purchase #5 $153.82   6.827%   $164.3213   $164.32   $164.30   $164.30  
  Purchase #6 $92.90   4.625%   $97.1966   $97.20   $97.20   $97.20  
  Purchase #7 $84.27   11.709%   $94.1372   $94.14   $94.15   $94.10  
  7 purchase totals = $972.63       $1,046.7114   $1,046.72   $1,046.75   $1,046.60