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 $167.83   10.621%   $185.6552   $185.66   $185.65   $185.70  
  Purchase #2 $226.37   8.477%   $245.5594   $245.56   $245.55   $245.60  
  Purchase #3 $200.84   8.438%   $217.7869   $217.79   $217.80   $217.80  
  Purchase #4 $126.79   8.677%   $137.7916   $137.79   $137.80   $137.80  
  Purchase #5 $125.89   11.603%   $140.497   $140.50   $140.50   $140.50  
  Purchase #6 $130.61   4.550%   $136.5528   $136.55   $136.55   $136.60  
  Purchase #7 $173.53   9.508%   $190.0292   $190.03   $190.05   $190.00  
  7 purchase totals = $1,151.86       $1,253.8721   $1,253.88   $1,253.90   $1,254.00