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 $87.92   12.262%   $98.7008   $98.70   $98.70   $98.70  
  Purchase #2 $37.31   10.202%   $41.1164   $41.12   $41.10   $41.10  
  Purchase #3 $184.95   8.698%   $201.037   $201.04   $201.05   $201.00  
  Purchase #4 $127.45   6.275%   $135.4475   $135.45   $135.45   $135.40  
  Purchase #5 $199.39   11.710%   $222.7386   $222.74   $222.75   $222.70  
  Purchase #6 $152.28   13.795%   $173.287   $173.29   $173.30   $173.30  
  Purchase #7 $29.83   6.856%   $31.8751   $31.88   $31.90   $31.90  
  7 purchase totals = $819.13       $904.2024   $904.22   $904.25   $904.10