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 $50.38   6.176%   $53.4915   $53.49   $53.50   $53.50  
  Purchase #2 $208.44   11.586%   $232.5899   $232.59   $232.60   $232.60  
  Purchase #3 $209.86   10.757%   $232.4346   $232.43   $232.45   $232.40  
  Purchase #4 $61.65   7.850%   $66.4895   $66.49   $66.50   $66.50  
  Purchase #5 $191.91   4.616%   $200.7686   $200.77   $200.75   $200.80  
  Purchase #6 $87.78   12.468%   $98.7244   $98.72   $98.70   $98.70  
  Purchase #7 $142.51   11.623%   $159.0739   $159.07   $159.05   $159.10  
  7 purchase totals = $952.53       $1,043.5724   $1,043.56   $1,043.55   $1,043.60