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 $60.58   11.121%   $67.3171   $67.32   $67.30   $67.30  
  Purchase #2 $227.87   5.801%   $241.0887   $241.09   $241.10   $241.10  
  Purchase #3 $98.68   6.376%   $104.9718   $104.97   $104.95   $105.00  
  Purchase #4 $172.56   12.291%   $193.7693   $193.77   $193.75   $193.80  
  Purchase #5 $225.27   6.403%   $239.694   $239.69   $239.70   $239.70  
  Purchase #6 $30.87   12.130%   $34.6145   $34.61   $34.60   $34.60  
  Purchase #7 $70.41   9.404%   $77.0314   $77.03   $77.05   $77.00  
  7 purchase totals = $886.24       $958.4868   $958.48   $958.45   $958.50