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	$7.25	3.385%	$7.4954	$7.50	$7.50	$7.50
Purchase #2	$137.58	13.589%	$156.2757	$156.28	$156.30	$156.30
Purchase #3	$145.39	4.694%	$152.2146	$152.21	$152.20	$152.20
Purchase #4	$232.67	12.640%	$262.0795	$262.08	$262.10	$262.10
Purchase #5	$100.51	3.399%	$103.9263	$103.93	$103.95	$103.90
Purchase #6	$210.83	13.862%	$240.0553	$240.06	$240.05	$240.10
Purchase #7	$239.63	4.653%	$250.78	$250.78	$250.80	$250.80
7 purchase totals =	$1,073.86		$1,172.8268	$1,172.84	$1,172.90	$1,172.90