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	$74.80	9.293%	$81.7512	$81.75	$81.75	$81.80
Purchase #2	$140.62	3.799%	$145.9622	$145.96	$145.95	$146.00
Purchase #3	$229.81	6.399%	$244.5155	$244.52	$244.50	$244.50
Purchase #4	$249.55	13.224%	$282.5505	$282.55	$282.55	$282.60
Purchase #5	$38.42	11.193%	$42.7204	$42.72	$42.70	$42.70
Purchase #6	$173.41	3.774%	$179.9545	$179.95	$179.95	$180.00
Purchase #7	$139.71	4.751%	$146.3476	$146.35	$146.35	$146.30
7 purchase totals =	$1,046.32		$1,123.8019	$1,123.80	$1,123.75	$1,123.90