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	$158.67	13.156%	$179.5446	$179.54	$179.55	$179.50
Purchase #2	$19.60	3.478%	$20.2817	$20.28	$20.30	$20.30
Purchase #3	$203.43	6.401%	$216.4516	$216.45	$216.45	$216.50
Purchase #4	$218.28	5.209%	$229.6502	$229.65	$229.65	$229.70
Purchase #5	$165.71	8.771%	$180.2444	$180.24	$180.25	$180.20
Purchase #6	$39.95	6.434%	$42.5204	$42.52	$42.50	$42.50
Purchase #7	$211.90	12.470%	$238.3239	$238.32	$238.30	$238.30
7 purchase totals =	$1,017.54		$1,107.0168	$1,107.00	$1,107.00	$1,107.00