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 $34.61   11.611%   $38.6286   $38.63   $38.65   $38.60  
  Purchase #2 $220.62   7.646%   $237.4886   $237.49   $237.50   $237.50  
  Purchase #3 $235.30   3.696%   $243.9967   $244.00   $244.00   $244.00  
  Purchase #4 $158.57   12.394%   $178.2232   $178.22   $178.20   $178.20  
  Purchase #5 $62.67   4.870%   $65.722   $65.72   $65.70   $65.70  
  Purchase #6 $219.41   5.615%   $231.7299   $231.73   $231.75   $231.70  
  Purchase #7 $210.33   3.365%   $217.4076   $217.41   $217.40   $217.40  
  7 purchase totals = $1,141.51       $1,213.1966   $1,213.20   $1,213.20   $1,213.10