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 $55.84   13.166%   $63.1919   $63.19   $63.20   $63.20  
  Purchase #2 $124.85   11.254%   $138.9006   $138.90   $138.90   $138.90  
  Purchase #3 $49.85   5.711%   $52.6969   $52.70   $52.70   $52.70  
  Purchase #4 $42.71   8.262%   $46.2387   $46.24   $46.25   $46.20  
  Purchase #5 $48.69   11.661%   $54.3677   $54.37   $54.35   $54.40  
  Purchase #6 $178.35   8.558%   $193.6132   $193.61   $193.60   $193.60  
  Purchase #7 $186.73   13.183%   $211.3466   $211.35   $211.35   $211.30  
  7 purchase totals = $687.02       $760.3556   $760.36   $760.35   $760.30