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	$180.33	10.623%	$199.4865	$199.49	$199.50	$199.50
Purchase #2	$223.25	12.595%	$251.3683	$251.37	$251.35	$251.40
Purchase #3	$151.57	8.557%	$164.5398	$164.54	$164.55	$164.50
Purchase #4	$182.26	4.645%	$190.726	$190.73	$190.75	$190.70
Purchase #5	$58.88	3.651%	$61.0297	$61.03	$61.05	$61.00
Purchase #6	$197.31	13.224%	$223.4023	$223.40	$223.40	$223.40
Purchase #7	$90.42	10.770%	$100.1582	$100.16	$100.15	$100.20
7 purchase totals =	$1,084.02		$1,190.7108	$1,190.72	$1,190.75	$1,190.70