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	$223.28	11.142%	$248.1579	$248.16	$248.15	$248.20
Purchase #2	$69.96	5.303%	$73.67	$73.67	$73.65	$73.70
Purchase #3	$70.71	7.617%	$76.096	$76.10	$76.10	$76.10
Purchase #4	$35.61	5.234%	$37.4738	$37.47	$37.45	$37.50
Purchase #5	$71.72	12.168%	$80.4469	$80.45	$80.45	$80.40
Purchase #6	$6.34	8.132%	$6.8556	$6.86	$6.85	$6.90
Purchase #7	$54.25	10.283%	$59.8285	$59.83	$59.85	$59.80
7 purchase totals =	$531.87		$582.5287	$582.54	$582.50	$582.60