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	$153.89	11.468%	$171.5381	$171.54	$171.55	$171.50
Purchase #2	$33.45	13.477%	$37.9581	$37.96	$37.95	$38.00
Purchase #3	$48.31	12.251%	$54.2285	$54.23	$54.25	$54.20
Purchase #4	$13.54	11.146%	$15.0492	$15.05	$15.05	$15.00
Purchase #5	$7.42	6.371%	$7.8927	$7.89	$7.90	$7.90
Purchase #6	$54.73	5.552%	$57.7686	$57.77	$57.75	$57.80
Purchase #7	$186.72	13.465%	$211.8618	$211.86	$211.85	$211.90
7 purchase totals =	$498.06		$556.2970	$556.30	$556.30	$556.30