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 $51.85   13.716%   $58.9617   $58.96   $58.95   $59.00  
  Purchase #2 $154.36   12.537%   $173.7121   $173.71   $173.70   $173.70  
  Purchase #3 $63.59   7.559%   $68.3968   $68.40   $68.40   $68.40  
  Purchase #4 $14.59   4.594%   $15.2603   $15.26   $15.25   $15.30  
  Purchase #5 $96.94   12.456%   $109.0148   $109.01   $109.00   $109.00  
  Purchase #6 $135.57   9.316%   $148.1997   $148.20   $148.20   $148.20  
  Purchase #7 $208.57   8.215%   $225.704   $225.70   $225.70   $225.70  
  7 purchase totals = $725.47       $799.2494   $799.24   $799.20   $799.30