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 $58.38   6.343%   $62.083   $62.08   $62.10   $62.10  
  Purchase #2 $237.96   7.234%   $255.174   $255.17   $255.15   $255.20  
  Purchase #3 $213.62   6.361%   $227.2084   $227.21   $227.20   $227.20  
  Purchase #4 $26.99   5.338%   $28.4307   $28.43   $28.45   $28.40  
  Purchase #5 $163.96   10.682%   $181.4742   $181.47   $181.45   $181.50  
  Purchase #6 $234.67   10.544%   $259.4136   $259.41   $259.40   $259.40  
  Purchase #7 $164.47   12.572%   $185.1472   $185.15   $185.15   $185.10  
  7 purchase totals = $1,100.05       $1,198.9311   $1,198.92   $1,198.90   $1,198.90