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	$180.44	4.845%	$189.1823	$189.18	$189.20	$189.20
Purchase #2	$58.88	5.840%	$62.3186	$62.32	$62.30	$62.30
Purchase #3	$73.56	12.385%	$82.6704	$82.67	$82.65	$82.70
Purchase #4	$151.95	3.678%	$157.5387	$157.54	$157.55	$157.50
Purchase #5	$61.99	12.698%	$69.8615	$69.86	$69.85	$69.90
Purchase #6	$84.57	7.388%	$90.818	$90.82	$90.80	$90.80
Purchase #7	$222.65	11.866%	$249.0696	$249.07	$249.05	$249.10
7 purchase totals =	$834.04		$901.4591	$901.46	$901.40	$901.50