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	$35.47	9.156%	$38.7176	$38.72	$38.70	$38.70
Purchase #2	$216.99	7.705%	$233.7091	$233.71	$233.70	$233.70
Purchase #3	$226.39	7.198%	$242.6856	$242.69	$242.70	$242.70
Purchase #4	$85.49	4.664%	$89.4773	$89.48	$89.50	$89.50
Purchase #5	$14.33	10.412%	$15.822	$15.82	$15.80	$15.80
Purchase #6	$246.28	12.677%	$277.5009	$277.50	$277.50	$277.50
Purchase #7	$24.51	3.659%	$25.4068	$25.41	$25.40	$25.40
7 purchase totals =	$849.46		$923.3193	$923.33	$923.30	$923.30