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 $94.74   7.782%   $102.1127   $102.11   $102.10   $102.10  
  Purchase #2 $243.31   6.298%   $258.6337   $258.63   $258.65   $258.60  
  Purchase #3 $61.61   13.211%   $69.7493   $69.75   $69.75   $69.70  
  Purchase #4 $51.40   10.286%   $56.687   $56.69   $56.70   $56.70  
  Purchase #5 $249.75   8.597%   $271.221   $271.22   $271.20   $271.20  
  Purchase #6 $139.93   6.554%   $149.101   $149.10   $149.10   $149.10  
  Purchase #7 $158.27   9.756%   $173.7108   $173.71   $173.70   $173.70  
  7 purchase totals = $999.01       $1,081.2155   $1,081.21   $1,081.20   $1,081.10