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	$130.37	4.519%	$136.2614	$136.26	$136.25	$136.30
Purchase #2	$191.30	11.627%	$213.5425	$213.54	$213.55	$213.50
Purchase #3	$57.62	6.120%	$61.1463	$61.15	$61.15	$61.10
Purchase #4	$139.84	3.602%	$144.877	$144.88	$144.90	$144.90
Purchase #5	$19.91	9.866%	$21.8743	$21.87	$21.85	$21.90
Purchase #6	$11.27	7.192%	$12.0805	$12.08	$12.10	$12.10
Purchase #7	$179.34	11.871%	$200.6295	$200.63	$200.65	$200.60
7 purchase totals =	$729.65		$790.4115	$790.41	$790.45	$790.40