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 $87.68   12.565%   $98.697   $98.70   $98.70   $98.70  
  Purchase #2 $193.63   4.853%   $203.0269   $203.03   $203.05   $203.00  
  Purchase #3 $125.61   8.526%   $136.3195   $136.32   $136.30   $136.30  
  Purchase #4 $233.86   9.220%   $255.4219   $255.42   $255.40   $255.40  
  Purchase #5 $73.49   13.555%   $83.4516   $83.45   $83.45   $83.50  
  Purchase #6 $238.29   5.841%   $252.2085   $252.21   $252.20   $252.20  
  Purchase #7 $44.61   9.151%   $48.6923   $48.69   $48.70   $48.70  
  7 purchase totals = $997.17       $1,077.8177   $1,077.82   $1,077.80   $1,077.80