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 $56.80   8.743%   $61.766   $61.77   $61.75   $61.80  
  Purchase #2 $78.75   11.137%   $87.5204   $87.52   $87.50   $87.50  
  Purchase #3 $49.51   4.696%   $51.835   $51.84   $51.85   $51.80  
  Purchase #4 $113.90   3.567%   $117.9628   $117.96   $117.95   $118.00  
  Purchase #5 $235.74   11.310%   $262.4022   $262.40   $262.40   $262.40  
  Purchase #6 $102.72   13.617%   $116.7074   $116.71   $116.70   $116.70  
  Purchase #7 $38.95   9.458%   $42.6339   $42.63   $42.65   $42.60  
  7 purchase totals = $676.37       $740.8277   $740.83   $740.80   $740.80