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	$243.66	10.316%	$268.796	$268.80	$268.80	$268.80
Purchase #2	$174.63	9.209%	$190.7117	$190.71	$190.70	$190.70
Purchase #3	$186.61	6.396%	$198.5456	$198.55	$198.55	$198.50
Purchase #4	$241.56	13.288%	$273.6585	$273.66	$273.65	$273.70
Purchase #5	$206.93	4.256%	$215.7369	$215.74	$215.75	$215.70
Purchase #6	$99.64	11.562%	$111.1604	$111.16	$111.15	$111.20
Purchase #7	$223.97	8.430%	$242.8507	$242.85	$242.85	$242.90
7 purchase totals =	$1,377.00		$1,501.4598	$1,501.47	$1,501.45	$1,501.50