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 $211.42   12.402%   $237.6403   $237.64   $237.65   $237.60  
  Purchase #2 $202.70   3.866%   $210.5364   $210.54   $210.55   $210.50  
  Purchase #3 $35.28   4.204%   $36.7632   $36.76   $36.75   $36.80  
  Purchase #4 $101.72   6.360%   $108.1894   $108.19   $108.20   $108.20  
  Purchase #5 $240.37   3.702%   $249.2685   $249.27   $249.25   $249.30  
  Purchase #6 $185.99   11.555%   $207.4811   $207.48   $207.50   $207.50  
  Purchase #7 $10.34   6.186%   $10.9796   $10.98   $11.00   $11.00  
  7 purchase totals = $987.82       $1,060.8585   $1,060.86   $1,060.90   $1,060.90