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 $140.86   8.615%   $152.9951   $153.00   $153.00   $153.00  
  Purchase #2 $200.53   8.164%   $216.9013   $216.90   $216.90   $216.90  
  Purchase #3 $34.38   10.391%   $37.9524   $37.95   $37.95   $38.00  
  Purchase #4 $203.60   6.391%   $216.6121   $216.61   $216.60   $216.60  
  Purchase #5 $193.51   4.766%   $202.7327   $202.73   $202.75   $202.70  
  Purchase #6 $162.94   5.239%   $171.4764   $171.48   $171.50   $171.50  
  Purchase #7 $231.34   8.309%   $250.562   $250.56   $250.55   $250.60  
  7 purchase totals = $1,167.16       $1,249.2320   $1,249.23   $1,249.25   $1,249.30