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	$10.65	4.664%	$11.1467	$11.15	$11.15	$11.10
Purchase #2	$238.95	7.372%	$256.5654	$256.57	$256.55	$256.60
Purchase #3	$80.53	3.829%	$83.6135	$83.61	$83.60	$83.60
Purchase #4	$244.90	12.477%	$275.4562	$275.46	$275.45	$275.50
Purchase #5	$54.57	6.314%	$58.0155	$58.02	$58.00	$58.00
Purchase #6	$35.97	7.697%	$38.7386	$38.74	$38.75	$38.70
Purchase #7	$85.81	4.730%	$89.8688	$89.87	$89.85	$89.90
7 purchase totals =	$751.38		$813.4047	$813.42	$813.35	$813.40