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 $58.93   6.140%   $62.5483   $62.55   $62.55   $62.50  
  Purchase #2 $241.43   12.605%   $271.8623   $271.86   $271.85   $271.90  
  Purchase #3 $67.58   12.336%   $75.9167   $75.92   $75.90   $75.90  
  Purchase #4 $132.93   13.224%   $150.5087   $150.51   $150.50   $150.50  
  Purchase #5 $202.90   9.789%   $222.7619   $222.76   $222.75   $222.80  
  Purchase #6 $246.45   5.351%   $259.6375   $259.64   $259.65   $259.60  
  Purchase #7 $226.87   8.744%   $246.7075   $246.71   $246.70   $246.70  
  7 purchase totals = $1,177.09       $1,289.9429   $1,289.95   $1,289.90   $1,289.90