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	$243.60	12.395%	$273.7942	$273.79	$273.80	$273.80
Purchase #2	$150.29	4.294%	$156.7435	$156.74	$156.75	$156.70
Purchase #3	$56.71	5.650%	$59.9141	$59.91	$59.90	$59.90
Purchase #4	$40.73	13.787%	$46.3454	$46.35	$46.35	$46.30
Purchase #5	$14.63	7.537%	$15.7327	$15.73	$15.75	$15.70
Purchase #6	$74.79	12.222%	$83.9308	$83.93	$83.95	$83.90
Purchase #7	$166.98	12.631%	$188.0712	$188.07	$188.05	$188.10
7 purchase totals =	$747.73		$824.5319	$824.52	$824.55	$824.40