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 $44.43   10.212%   $48.9672   $48.97   $48.95   $49.00  
  Purchase #2 $234.41   8.511%   $254.3606   $254.36   $254.35   $254.40  
  Purchase #3 $107.70   9.865%   $118.3246   $118.32   $118.30   $118.30  
  Purchase #4 $156.45   3.356%   $161.7005   $161.70   $161.70   $161.70  
  Purchase #5 $171.91   6.147%   $182.4773   $182.48   $182.50   $182.50  
  Purchase #6 $226.87   13.377%   $257.2184   $257.22   $257.20   $257.20  
  Purchase #7 $244.52   11.806%   $273.388   $273.39   $273.40   $273.40  
  7 purchase totals = $1,186.29       $1,296.4366   $1,296.44   $1,296.40   $1,296.50