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 $60.63   3.149%   $62.5392   $62.54   $62.55   $62.50  
  Purchase #2 $240.28   9.874%   $264.0052   $264.01   $264.00   $264.00  
  Purchase #3 $233.29   3.607%   $241.7048   $241.70   $241.70   $241.70  
  Purchase #4 $95.45   4.504%   $99.7491   $99.75   $99.75   $99.70  
  Purchase #5 $109.72   12.272%   $123.1848   $123.18   $123.20   $123.20  
  Purchase #6 $127.94   3.278%   $132.1339   $132.13   $132.15   $132.10  
  Purchase #7 $122.87   7.440%   $132.0115   $132.01   $132.00   $132.00  
  7 purchase totals = $990.18       $1,055.3285   $1,055.32   $1,055.35   $1,055.20