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 $197.45   13.256%   $223.624   $223.62   $223.60   $223.60  
  Purchase #2 $181.42   10.629%   $200.7031   $200.70   $200.70   $200.70  
  Purchase #3 $16.62   13.866%   $18.9245   $18.92   $18.90   $18.90  
  Purchase #4 $237.66   10.575%   $262.7925   $262.79   $262.80   $262.80  
  Purchase #5 $61.69   13.529%   $70.036   $70.04   $70.05   $70.00  
  Purchase #6 $46.46   7.672%   $50.0244   $50.02   $50.00   $50.00  
  Purchase #7 $69.79   3.195%   $72.0198   $72.02   $72.00   $72.00  
  7 purchase totals = $811.09       $898.1243   $898.11   $898.05   $898.00