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	$248.42	10.538%	$274.5985	$274.60	$274.60	$274.60
Purchase #2	$114.61	4.345%	$119.5898	$119.59	$119.60	$119.60
Purchase #3	$81.96	6.660%	$87.4185	$87.42	$87.40	$87.40
Purchase #4	$223.32	12.311%	$250.8129	$250.81	$250.80	$250.80
Purchase #5	$124.30	12.644%	$140.0165	$140.02	$140.00	$140.00
Purchase #6	$113.47	9.242%	$123.9569	$123.96	$123.95	$124.00
Purchase #7	$7.74	10.482%	$8.5513	$8.55	$8.55	$8.60
7 purchase totals =	$913.82		$1,004.9444	$1,004.95	$1,004.90	$1,005.00