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 $51.67   11.444%   $57.5831   $57.58   $57.60   $57.60  
  Purchase #2 $164.81   6.255%   $175.1189   $175.12   $175.10   $175.10  
  Purchase #3 $192.90   8.261%   $208.8355   $208.84   $208.85   $208.80  
  Purchase #4 $15.69   10.402%   $17.3221   $17.32   $17.30   $17.30  
  Purchase #5 $89.32   9.614%   $97.9072   $97.91   $97.90   $97.90  
  Purchase #6 $168.77   5.722%   $178.427   $178.43   $178.45   $178.40  
  Purchase #7 $35.84   3.199%   $36.9865   $36.99   $37.00   $37.00  
  7 purchase totals = $719.00       $772.1803   $772.19   $772.20   $772.10