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 $64.87   10.806%   $71.8799   $71.88   $71.90   $71.90  
  Purchase #2 $248.35   5.817%   $262.7965   $262.80   $262.80   $262.80  
  Purchase #3 $111.78   12.716%   $125.9939   $125.99   $126.00   $126.00  
  Purchase #4 $126.68   9.351%   $138.5258   $138.53   $138.55   $138.50  
  Purchase #5 $129.76   5.400%   $136.767   $136.77   $136.75   $136.80  
  Purchase #6 $202.50   6.550%   $215.7638   $215.76   $215.75   $215.80  
  Purchase #7 $49.92   5.436%   $52.6337   $52.63   $52.65   $52.60  
  7 purchase totals = $933.86       $1,004.3606   $1,004.36   $1,004.40   $1,004.40