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 $241.72   8.861%   $263.1388   $263.14   $263.15   $263.10  
  Purchase #2 $190.92   11.248%   $212.3947   $212.39   $212.40   $212.40  
  Purchase #3 $162.31   8.873%   $176.7118   $176.71   $176.70   $176.70  
  Purchase #4 $7.74   6.622%   $8.2525   $8.25   $8.25   $8.30  
  Purchase #5 $213.84   3.748%   $221.8547   $221.85   $221.85   $221.90  
  Purchase #6 $51.87   10.548%   $57.3412   $57.34   $57.35   $57.30  
  Purchase #7 $55.65   6.345%   $59.181   $59.18   $59.20   $59.20  
  7 purchase totals = $924.05       $998.8747   $998.86   $998.90   $998.90