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	$179.26	13.795%	$203.9889	$203.99	$204.00	$204.00
Purchase #2	$152.77	6.439%	$162.6069	$162.61	$162.60	$162.60
Purchase #3	$209.51	9.142%	$228.6634	$228.66	$228.65	$228.70
Purchase #4	$209.73	6.593%	$223.5575	$223.56	$223.55	$223.60
Purchase #5	$69.52	12.427%	$78.1593	$78.16	$78.15	$78.20
Purchase #6	$240.82	6.792%	$257.1765	$257.18	$257.20	$257.20
Purchase #7	$29.81	5.505%	$31.451	$31.45	$31.45	$31.50
7 purchase totals =	$1,091.42		$1,185.6035	$1,185.61	$1,185.60	$1,185.80