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 $226.82   3.726%   $235.2713   $235.27   $235.25   $235.30  
  Purchase #2 $10.26   4.431%   $10.7146   $10.71   $10.70   $10.70  
  Purchase #3 $149.76   10.111%   $164.9022   $164.90   $164.90   $164.90  
  Purchase #4 $53.27   5.573%   $56.2387   $56.24   $56.25   $56.20  
  Purchase #5 $82.58   12.161%   $92.6226   $92.62   $92.60   $92.60  
  Purchase #6 $152.80   6.626%   $162.9245   $162.92   $162.90   $162.90  
  Purchase #7 $132.89   12.438%   $149.4189   $149.42   $149.40   $149.40  
  7 purchase totals = $808.38       $872.0928   $872.08   $872.00   $872.00