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 $58.65   5.794%   $62.0482   $62.05   $62.05   $62.00  
  Purchase #2 $33.97   12.552%   $38.2339   $38.23   $38.25   $38.20  
  Purchase #3 $218.83   12.812%   $246.8665   $246.87   $246.85   $246.90  
  Purchase #4 $37.72   7.402%   $40.512   $40.51   $40.50   $40.50  
  Purchase #5 $46.42   11.618%   $51.8131   $51.81   $51.80   $51.80  
  Purchase #6 $6.98   5.371%   $7.3549   $7.35   $7.35   $7.40  
  Purchase #7 $223.98   9.606%   $245.4955   $245.50   $245.50   $245.50  
  7 purchase totals = $626.55       $692.3241   $692.32   $692.30   $692.30