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	$196.62	12.614%	$221.4216	$221.42	$221.40	$221.40
Purchase #2	$73.56	5.377%	$77.5153	$77.52	$77.50	$77.50
Purchase #3	$219.72	7.417%	$236.0166	$236.02	$236.00	$236.00
Purchase #4	$137.31	5.105%	$144.3197	$144.32	$144.30	$144.30
Purchase #5	$13.50	6.789%	$14.4165	$14.42	$14.40	$14.40
Purchase #6	$207.71	11.202%	$230.9777	$230.98	$231.00	$231.00
Purchase #7	$68.33	6.570%	$72.8193	$72.82	$72.80	$72.80
7 purchase totals =	$916.75		$997.4867	$997.50	$997.40	$997.40