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	$83.52	7.729%	$89.9753	$89.98	$90.00	$90.00
Purchase #2	$48.86	12.137%	$54.7901	$54.79	$54.80	$54.80
Purchase #3	$99.87	6.318%	$106.1798	$106.18	$106.20	$106.20
Purchase #4	$246.63	6.656%	$263.0457	$263.05	$263.05	$263.00
Purchase #5	$41.36	12.771%	$46.6421	$46.64	$46.65	$46.60
Purchase #6	$75.95	3.218%	$78.3941	$78.39	$78.40	$78.40
Purchase #7	$134.33	13.492%	$152.4538	$152.45	$152.45	$152.50
7 purchase totals =	$730.52		$791.4809	$791.48	$791.55	$791.50