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 $58.85   3.344%   $60.8179   $60.82   $60.80   $60.80  
  Purchase #2 $81.68   3.512%   $84.5486   $84.55   $84.55   $84.50  
  Purchase #3 $38.99   13.483%   $44.247   $44.25   $44.25   $44.20  
  Purchase #4 $211.47   9.549%   $231.6633   $231.66   $231.65   $231.70  
  Purchase #5 $243.40   9.440%   $266.377   $266.38   $266.40   $266.40  
  Purchase #6 $200.31   4.773%   $209.8708   $209.87   $209.85   $209.90  
  Purchase #7 $82.80   5.635%   $87.4658   $87.47   $87.45   $87.50  
  7 purchase totals = $917.50       $984.9904   $985.00   $984.95   $985.00