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 $51.32   9.622%   $56.258   $56.26   $56.25   $56.30  
  Purchase #2 $59.78   5.580%   $63.1157   $63.12   $63.10   $63.10  
  Purchase #3 $88.64   9.490%   $97.0519   $97.05   $97.05   $97.10  
  Purchase #4 $189.72   13.510%   $215.3512   $215.35   $215.35   $215.40  
  Purchase #5 $37.30   3.636%   $38.6562   $38.66   $38.65   $38.70  
  Purchase #6 $242.44   13.701%   $275.6567   $275.66   $275.65   $275.70  
  Purchase #7 $15.97   4.385%   $16.6703   $16.67   $16.65   $16.70  
  7 purchase totals = $685.17       $762.7600   $762.77   $762.70   $763.00