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 $214.47   10.728%   $237.4783   $237.48   $237.50   $237.50  
  Purchase #2 $155.94   13.191%   $176.51   $176.51   $176.50   $176.50  
  Purchase #3 $205.41   7.119%   $220.0331   $220.03   $220.05   $220.00  
  Purchase #4 $34.44   9.536%   $37.7242   $37.72   $37.70   $37.70  
  Purchase #5 $205.26   7.564%   $220.7859   $220.79   $220.80   $220.80  
  Purchase #6 $226.92   10.156%   $249.966   $249.97   $249.95   $250.00  
  Purchase #7 $209.51   8.532%   $227.3854   $227.39   $227.40   $227.40  
  7 purchase totals = $1,251.95       $1,369.8829   $1,369.89   $1,369.90   $1,369.90