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 $226.68   13.643%   $257.606   $257.61   $257.60   $257.60  
  Purchase #2 $103.28   8.263%   $111.814   $111.81   $111.80   $111.80  
  Purchase #3 $242.56   6.211%   $257.6254   $257.63   $257.65   $257.60  
  Purchase #4 $239.36   6.226%   $254.2626   $254.26   $254.25   $254.30  
  Purchase #5 $60.36   10.838%   $66.9018   $66.90   $66.90   $66.90  
  Purchase #6 $172.53   9.654%   $189.186   $189.19   $189.20   $189.20  
  Purchase #7 $67.33   7.350%   $72.2788   $72.28   $72.30   $72.30  
  7 purchase totals = $1,112.10       $1,209.6746   $1,209.68   $1,209.70   $1,209.70