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 $75.97   12.193%   $85.233   $85.23   $85.25   $85.20  
  Purchase #2 $226.42   4.568%   $236.7629   $236.76   $236.75   $236.80  
  Purchase #3 $133.41   10.237%   $147.0672   $147.07   $147.05   $147.10  
  Purchase #4 $90.77   11.247%   $100.9789   $100.98   $101.00   $101.00  
  Purchase #5 $33.68   6.829%   $35.98   $35.98   $36.00   $36.00  
  Purchase #6 $153.91   3.704%   $159.6108   $159.61   $159.60   $159.60  
  Purchase #7 $244.89   8.658%   $266.0926   $266.09   $266.10   $266.10  
  7 purchase totals = $959.05       $1,031.7254   $1,031.72   $1,031.75   $1,031.80