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 $162.91   8.561%   $176.8567   $176.86   $176.85   $176.90  
  Purchase #2 $245.40   13.673%   $278.9535   $278.95   $278.95   $279.00  
  Purchase #3 $196.85   8.654%   $213.8854   $213.89   $213.90   $213.90  
  Purchase #4 $121.33   7.161%   $130.0184   $130.02   $130.00   $130.00  
  Purchase #5 $31.91   9.473%   $34.9328   $34.93   $34.95   $34.90  
  Purchase #6 $246.44   5.649%   $260.3614   $260.36   $260.35   $260.40  
  Purchase #7 $197.83   4.452%   $206.6374   $206.64   $206.65   $206.60  
  7 purchase totals = $1,202.67       $1,301.6456   $1,301.65   $1,301.65   $1,301.70