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 $212.43   8.548%   $230.5885   $230.59   $230.60   $230.60  
  Purchase #2 $229.50   7.141%   $245.8886   $245.89   $245.90   $245.90  
  Purchase #3 $190.33   13.191%   $215.4364   $215.44   $215.45   $215.40  
  Purchase #4 $23.89   12.727%   $26.9305   $26.93   $26.95   $26.90  
  Purchase #5 $195.92   3.451%   $202.6812   $202.68   $202.70   $202.70  
  Purchase #6 $58.42   3.329%   $60.3648   $60.36   $60.35   $60.40  
  Purchase #7 $200.54   7.753%   $216.0879   $216.09   $216.10   $216.10  
  7 purchase totals = $1,111.03       $1,197.9779   $1,197.98   $1,198.05   $1,198.00