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	$105.74	6.654%	$112.7759	$112.78	$112.80	$112.80
Purchase #2	$175.82	3.761%	$182.4326	$182.43	$182.45	$182.40
Purchase #3	$74.54	8.117%	$80.5904	$80.59	$80.60	$80.60
Purchase #4	$188.84	11.380%	$210.33	$210.33	$210.35	$210.30
Purchase #5	$237.56	7.389%	$255.1133	$255.11	$255.10	$255.10
Purchase #6	$101.42	8.310%	$109.848	$109.85	$109.85	$109.80
Purchase #7	$191.69	13.405%	$217.386	$217.39	$217.40	$217.40
7 purchase totals =	$1,075.61		$1,168.4762	$1,168.48	$1,168.55	$1,168.40