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 $98.38   5.737%   $104.0241   $104.02   $104.00   $104.00  
  Purchase #2 $241.40   13.493%   $273.9721   $273.97   $273.95   $274.00  
  Purchase #3 $194.98   6.620%   $207.8877   $207.89   $207.90   $207.90  
  Purchase #4 $165.41   13.244%   $187.3169   $187.32   $187.30   $187.30  
  Purchase #5 $200.61   13.437%   $227.566   $227.57   $227.55   $227.60  
  Purchase #6 $136.80   5.607%   $144.4704   $144.47   $144.45   $144.50  
  Purchase #7 $143.59   10.452%   $158.598   $158.60   $158.60   $158.60  
  7 purchase totals = $1,181.17       $1,303.8352   $1,303.84   $1,303.75   $1,303.90