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 $61.36   13.348%   $69.5503   $69.55   $69.55   $69.60  
  Purchase #2 $191.42   12.353%   $215.0661   $215.07   $215.05   $215.10  
  Purchase #3 $79.75   5.161%   $83.8659   $83.87   $83.85   $83.90  
  Purchase #4 $215.25   7.105%   $230.5435   $230.54   $230.55   $230.50  
  Purchase #5 $14.80   3.505%   $15.3187   $15.32   $15.30   $15.30  
  Purchase #6 $132.57   7.864%   $142.9953   $143.00   $143.00   $143.00  
  Purchase #7 $82.84   13.757%   $94.2363   $94.24   $94.25   $94.20  
  7 purchase totals = $777.99       $851.5761   $851.59   $851.55   $851.60