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 $149.49   7.522%   $160.7346   $160.73   $160.75   $160.70  
  Purchase #2 $71.64   12.580%   $80.6523   $80.65   $80.65   $80.70  
  Purchase #3 $168.28   8.790%   $183.0718   $183.07   $183.05   $183.10  
  Purchase #4 $196.38   6.174%   $208.5045   $208.50   $208.50   $208.50  
  Purchase #5 $101.62   11.462%   $113.2677   $113.27   $113.25   $113.30  
  Purchase #6 $224.80   9.324%   $245.7604   $245.76   $245.75   $245.80  
  Purchase #7 $46.32   5.865%   $49.0367   $49.04   $49.05   $49.00  
  7 purchase totals = $958.53       $1,041.0280   $1,041.02   $1,041.00   $1,041.10