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 $93.48   12.576%   $105.236   $105.24   $105.25   $105.20  
  Purchase #2 $215.50   4.298%   $224.7622   $224.76   $224.75   $224.80  
  Purchase #3 $44.90   4.845%   $47.0754   $47.08   $47.10   $47.10  
  Purchase #4 $184.27   9.483%   $201.7443   $201.74   $201.75   $201.70  
  Purchase #5 $234.45   4.717%   $245.509   $245.51   $245.50   $245.50  
  Purchase #6 $108.50   3.855%   $112.6827   $112.68   $112.70   $112.70  
  Purchase #7 $52.69   7.620%   $56.705   $56.71   $56.70   $56.70  
  7 purchase totals = $933.79       $993.7146   $993.72   $993.75   $993.70