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 $194.69   8.366%   $210.9778   $210.98   $211.00   $211.00  
  Purchase #2 $156.87   11.221%   $174.4724   $174.47   $174.45   $174.50  
  Purchase #3 $30.77   10.316%   $33.9442   $33.94   $33.95   $33.90  
  Purchase #4 $155.27   13.606%   $176.396   $176.40   $176.40   $176.40  
  Purchase #5 $12.54   7.612%   $13.4945   $13.49   $13.50   $13.50  
  Purchase #6 $182.42   8.779%   $198.4347   $198.43   $198.45   $198.40  
  Purchase #7 $224.84   7.492%   $241.685   $241.69   $241.70   $241.70  
  7 purchase totals = $957.40       $1,049.4046   $1,049.40   $1,049.45   $1,049.40