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 $181.68   12.698%   $204.7497   $204.75   $204.75   $204.70  
  Purchase #2 $119.70   13.434%   $135.7805   $135.78   $135.80   $135.80  
  Purchase #3 $130.53   4.374%   $136.2394   $136.24   $136.25   $136.20  
  Purchase #4 $139.42   12.672%   $157.0873   $157.09   $157.10   $157.10  
  Purchase #5 $226.73   5.505%   $239.2115   $239.21   $239.20   $239.20  
  Purchase #6 $13.46   13.157%   $15.2309   $15.23   $15.25   $15.20  
  Purchase #7 $212.33   6.437%   $225.9977   $226.00   $226.00   $226.00  
  7 purchase totals = $1,023.85       $1,114.2970   $1,114.30   $1,114.35   $1,114.20