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 $64.47   6.232%   $68.4878   $68.49   $68.50   $68.50  
  Purchase #2 $106.25   12.312%   $119.3315   $119.33   $119.35   $119.30  
  Purchase #3 $85.69   8.781%   $93.2144   $93.21   $93.20   $93.20  
  Purchase #4 $60.38   3.645%   $62.5809   $62.58   $62.60   $62.60  
  Purchase #5 $45.33   6.408%   $48.2347   $48.23   $48.25   $48.20  
  Purchase #6 $54.78   5.449%   $57.765   $57.77   $57.75   $57.80  
  Purchase #7 $77.47   8.269%   $83.876   $83.88   $83.90   $83.90  
  7 purchase totals = $494.37       $533.4903   $533.49   $533.55   $533.50