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 $61.97   10.520%   $68.4892   $68.49   $68.50   $68.50  
  Purchase #2 $248.55   6.785%   $265.4141   $265.41   $265.40   $265.40  
  Purchase #3 $213.43   13.479%   $242.1982   $242.20   $242.20   $242.20  
  Purchase #4 $23.61   5.757%   $24.9692   $24.97   $24.95   $25.00  
  Purchase #5 $62.61   7.367%   $67.2225   $67.22   $67.20   $67.20  
  Purchase #6 $73.91   5.298%   $77.8258   $77.83   $77.85   $77.80  
  Purchase #7 $210.43   8.727%   $228.7942   $228.79   $228.80   $228.80  
  7 purchase totals = $894.51       $974.9132   $974.91   $974.90   $974.90