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 $58.40   12.289%   $65.5768   $65.58   $65.60   $65.60  
  Purchase #2 $94.95   3.136%   $97.9276   $97.93   $97.95   $97.90  
  Purchase #3 $225.34   4.718%   $235.9715   $235.97   $235.95   $236.00  
  Purchase #4 $232.66   8.600%   $252.6688   $252.67   $252.65   $252.70  
  Purchase #5 $206.27   13.355%   $233.8174   $233.82   $233.80   $233.80  
  Purchase #6 $57.49   5.133%   $60.441   $60.44   $60.45   $60.40  
  Purchase #7 $72.79   5.840%   $77.0409   $77.04   $77.05   $77.00  
  7 purchase totals = $947.90       $1,023.4440   $1,023.45   $1,023.45   $1,023.40