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	$245.31	4.229%	$255.6842	$255.68	$255.70	$255.70
Purchase #2	$221.65	7.735%	$238.7946	$238.79	$238.80	$238.80
Purchase #3	$120.36	4.596%	$125.8917	$125.89	$125.90	$125.90
Purchase #4	$158.94	12.758%	$179.2176	$179.22	$179.20	$179.20
Purchase #5	$137.26	5.179%	$144.3687	$144.37	$144.35	$144.40
Purchase #6	$87.53	3.738%	$90.8019	$90.80	$90.80	$90.80
Purchase #7	$35.57	4.309%	$37.1027	$37.10	$37.10	$37.10
7 purchase totals =	$1,006.62		$1,071.8614	$1,071.85	$1,071.85	$1,071.90