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 $213.61   6.141%   $226.7278   $226.73   $226.75   $226.70  
  Purchase #2 $200.59   9.166%   $218.9761   $218.98   $219.00   $219.00  
  Purchase #3 $236.83   13.545%   $268.9086   $268.91   $268.90   $268.90  
  Purchase #4 $23.29   7.343%   $25.0002   $25.00   $25.00   $25.00  
  Purchase #5 $145.87   4.429%   $152.3306   $152.33   $152.35   $152.30  
  Purchase #6 $83.26   3.595%   $86.2532   $86.25   $86.25   $86.30  
  Purchase #7 $248.29   9.608%   $272.1457   $272.15   $272.15   $272.10  
  7 purchase totals = $1,151.74       $1,250.3422   $1,250.35   $1,250.40   $1,250.30