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 $241.30   10.844%   $267.4666   $267.47   $267.45   $267.50  
  Purchase #2 $159.34   11.692%   $177.97   $177.97   $177.95   $178.00  
  Purchase #3 $182.43   8.587%   $198.0953   $198.10   $198.10   $198.10  
  Purchase #4 $35.29   12.437%   $39.679   $39.68   $39.70   $39.70  
  Purchase #5 $15.26   13.162%   $17.2685   $17.27   $17.25   $17.30  
  Purchase #6 $209.85   13.233%   $237.6195   $237.62   $237.60   $237.60  
  Purchase #7 $144.73   13.853%   $164.7794   $164.78   $164.80   $164.80  
  7 purchase totals = $988.20       $1,102.8783   $1,102.89   $1,102.85   $1,103.00