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 $183.62   12.677%   $206.8975   $206.90   $206.90   $206.90  
  Purchase #2 $56.29   12.452%   $63.2992   $63.30   $63.30   $63.30  
  Purchase #3 $13.70   10.436%   $15.1297   $15.13   $15.15   $15.10  
  Purchase #4 $200.41   6.325%   $213.0859   $213.09   $213.10   $213.10  
  Purchase #5 $209.32   8.142%   $226.3628   $226.36   $226.35   $226.40  
  Purchase #6 $147.54   9.326%   $161.2996   $161.30   $161.30   $161.30  
  Purchase #7 $25.76   9.319%   $28.1606   $28.16   $28.15   $28.20  
  7 purchase totals = $836.64       $914.2353   $914.24   $914.25   $914.30