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 $54.78   12.534%   $61.6461   $61.65   $61.65   $61.60  
  Purchase #2 $172.85   11.339%   $192.4495   $192.45   $192.45   $192.40  
  Purchase #3 $232.46   5.598%   $245.4731   $245.47   $245.45   $245.50  
  Purchase #4 $215.34   3.697%   $223.3011   $223.30   $223.30   $223.30  
  Purchase #5 $95.43   10.771%   $105.7088   $105.71   $105.70   $105.70  
  Purchase #6 $141.75   8.778%   $154.1928   $154.19   $154.20   $154.20  
  Purchase #7 $249.47   3.868%   $259.1195   $259.12   $259.10   $259.10  
  7 purchase totals = $1,162.08       $1,241.8909   $1,241.89   $1,241.85   $1,241.80