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 $111.45   12.395%   $125.2642   $125.26   $125.25   $125.30  
  Purchase #2 $26.43   12.344%   $29.6925   $29.69   $29.70   $29.70  
  Purchase #3 $79.59   6.704%   $84.9257   $84.93   $84.95   $84.90  
  Purchase #4 $48.47   9.868%   $53.253   $53.25   $53.25   $53.30  
  Purchase #5 $133.36   12.470%   $149.99   $149.99   $150.00   $150.00  
  Purchase #6 $46.26   7.347%   $49.6587   $49.66   $49.65   $49.70  
  Purchase #7 $250.84   8.298%   $271.6547   $271.65   $271.65   $271.70  
  7 purchase totals = $696.40       $764.4388   $764.43   $764.45   $764.60