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 $57.66   9.515%   $63.1463   $63.15   $63.15   $63.10  
  Purchase #2 $82.88   8.227%   $89.6985   $89.70   $89.70   $89.70  
  Purchase #3 $117.94   12.457%   $132.6318   $132.63   $132.65   $132.60  
  Purchase #4 $179.81   12.872%   $202.9551   $202.96   $202.95   $203.00  
  Purchase #5 $177.88   13.716%   $202.278   $202.28   $202.30   $202.30  
  Purchase #6 $7.85   13.395%   $8.9015   $8.90   $8.90   $8.90  
  Purchase #7 $47.36   4.728%   $49.5992   $49.60   $49.60   $49.60  
  7 purchase totals = $671.38       $749.2104   $749.22   $749.25   $749.20