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 $205.34   10.718%   $227.3483   $227.35   $227.35   $227.30  
  Purchase #2 $116.97   8.831%   $127.2996   $127.30   $127.30   $127.30  
  Purchase #3 $20.41   3.732%   $21.1717   $21.17   $21.15   $21.20  
  Purchase #4 $203.77   3.807%   $211.5275   $211.53   $211.55   $211.50  
  Purchase #5 $109.40   9.628%   $119.933   $119.93   $119.95   $119.90  
  Purchase #6 $26.40   5.246%   $27.7849   $27.78   $27.80   $27.80  
  Purchase #7 $55.99   11.286%   $62.309   $62.31   $62.30   $62.30  
  7 purchase totals = $738.28       $797.3740   $797.37   $797.40   $797.30