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 $62.28   5.340%   $65.6058   $65.61   $65.60   $65.60  
  Purchase #2 $14.87   11.263%   $16.5448   $16.54   $16.55   $16.50  
  Purchase #3 $158.37   3.332%   $163.6469   $163.65   $163.65   $163.60  
  Purchase #4 $117.50   4.400%   $122.67   $122.67   $122.65   $122.70  
  Purchase #5 $25.76   4.526%   $26.9259   $26.93   $26.95   $26.90  
  Purchase #6 $154.85   8.133%   $167.444   $167.44   $167.45   $167.40  
  Purchase #7 $180.95   8.225%   $195.8331   $195.83   $195.85   $195.80  
  7 purchase totals = $714.58       $758.6705   $758.67   $758.70   $758.50