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 $69.91   10.410%   $77.1876   $77.19   $77.20   $77.20  
  Purchase #2 $91.44   4.170%   $95.253   $95.25   $95.25   $95.30  
  Purchase #3 $147.47   3.602%   $152.7819   $152.78   $152.80   $152.80  
  Purchase #4 $231.75   7.830%   $249.896   $249.90   $249.90   $249.90  
  Purchase #5 $108.67   11.142%   $120.778   $120.78   $120.80   $120.80  
  Purchase #6 $97.74   6.842%   $104.4274   $104.43   $104.45   $104.40  
  Purchase #7 $57.68   12.280%   $64.7631   $64.76   $64.75   $64.80  
  7 purchase totals = $804.66       $865.0870   $865.09   $865.15   $865.20