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 $236.63   13.457%   $268.4733   $268.47   $268.45   $268.50  
  Purchase #2 $207.69   11.518%   $231.6117   $231.61   $231.60   $231.60  
  Purchase #3 $87.49   8.581%   $94.9975   $95.00   $95.00   $95.00  
  Purchase #4 $134.76   12.629%   $151.7788   $151.78   $151.80   $151.80  
  Purchase #5 $7.75   8.868%   $8.4373   $8.44   $8.45   $8.40  
  Purchase #6 $145.60   12.129%   $163.2598   $163.26   $163.25   $163.30  
  Purchase #7 $149.99   5.412%   $158.1075   $158.11   $158.10   $158.10  
  7 purchase totals = $969.91       $1,076.6659   $1,076.67   $1,076.65   $1,076.70