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 $158.90   4.722%   $166.4033   $166.40   $166.40   $166.40  
  Purchase #2 $101.95   6.675%   $108.7552   $108.76   $108.75   $108.80  
  Purchase #3 $163.42   13.569%   $185.5945   $185.59   $185.60   $185.60  
  Purchase #4 $192.75   7.465%   $207.1388   $207.14   $207.15   $207.10  
  Purchase #5 $25.87   11.197%   $28.7667   $28.77   $28.75   $28.80  
  Purchase #6 $161.94   5.505%   $170.8548   $170.85   $170.85   $170.90  
  Purchase #7 $27.78   13.489%   $31.5272   $31.53   $31.55   $31.50  
  7 purchase totals = $832.61       $899.0405   $899.04   $899.05   $899.10