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 $152.81   5.866%   $161.7738   $161.77   $161.75   $161.80  
  Purchase #2 $104.46   10.392%   $115.3155   $115.32   $115.30   $115.30  
  Purchase #3 $92.61   6.739%   $98.851   $98.85   $98.85   $98.90  
  Purchase #4 $247.62   10.300%   $273.1249   $273.12   $273.10   $273.10  
  Purchase #5 $60.91   9.505%   $66.6995   $66.70   $66.70   $66.70  
  Purchase #6 $126.59   6.270%   $134.5272   $134.53   $134.55   $134.50  
  Purchase #7 $126.75   4.754%   $132.7757   $132.78   $132.80   $132.80  
  7 purchase totals = $911.75       $983.0676   $983.07   $983.05   $983.10