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 $54.38   13.557%   $61.7523   $61.75   $61.75   $61.80  
  Purchase #2 $109.47   7.328%   $117.492   $117.49   $117.50   $117.50  
  Purchase #3 $58.49   7.723%   $63.0072   $63.01   $63.00   $63.00  
  Purchase #4 $77.75   6.789%   $83.0284   $83.03   $83.05   $83.00  
  Purchase #5 $119.85   3.451%   $123.986   $123.99   $124.00   $124.00  
  Purchase #6 $146.80   13.286%   $166.3038   $166.30   $166.30   $166.30  
  Purchase #7 $52.43   13.538%   $59.528   $59.53   $59.55   $59.50  
  7 purchase totals = $619.17       $675.0977   $675.10   $675.15   $675.10