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 $161.28   7.179%   $172.8583   $172.86   $172.85   $172.90  
  Purchase #2 $78.64   10.805%   $87.1371   $87.14   $87.15   $87.10  
  Purchase #3 $9.57   6.361%   $10.1787   $10.18   $10.20   $10.20  
  Purchase #4 $221.79   12.732%   $250.0283   $250.03   $250.05   $250.00  
  Purchase #5 $230.42   12.553%   $259.3446   $259.34   $259.35   $259.30  
  Purchase #6 $15.76   3.870%   $16.3699   $16.37   $16.35   $16.40  
  Purchase #7 $184.81   13.198%   $209.2012   $209.20   $209.20   $209.20  
  7 purchase totals = $902.27       $1,005.1181   $1,005.12   $1,005.15   $1,005.10