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	$179.93	6.144%	$190.9849	$190.98	$191.00	$191.00
Purchase #2	$178.50	11.718%	$199.4166	$199.42	$199.40	$199.40
Purchase #3	$233.30	12.419%	$262.2735	$262.27	$262.25	$262.30
Purchase #4	$182.47	7.475%	$196.1096	$196.11	$196.10	$196.10
Purchase #5	$93.78	13.505%	$106.445	$106.45	$106.45	$106.40
Purchase #6	$159.58	6.392%	$169.7804	$169.78	$169.80	$169.80
Purchase #7	$191.46	6.682%	$204.2534	$204.25	$204.25	$204.30
7 purchase totals =	$1,219.02		$1,329.2634	$1,329.26	$1,329.25	$1,329.30