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 $59.81   5.401%   $63.0403   $63.04   $63.05   $63.00  
  Purchase #2 $166.38   10.548%   $183.9298   $183.93   $183.95   $183.90  
  Purchase #3 $9.96   9.829%   $10.939   $10.94   $10.95   $10.90  
  Purchase #4 $150.66   5.607%   $159.1075   $159.11   $159.10   $159.10  
  Purchase #5 $236.63   11.237%   $263.2201   $263.22   $263.20   $263.20  
  Purchase #6 $54.32   12.649%   $61.1909   $61.19   $61.20   $61.20  
  Purchase #7 $93.67   13.361%   $106.1852   $106.19   $106.20   $106.20  
  7 purchase totals = $771.43       $847.6128   $847.62   $847.65   $847.50