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	$236.98	7.705%	$255.2393	$255.24	$255.25	$255.20
Purchase #2	$227.62	8.666%	$247.3455	$247.35	$247.35	$247.30
Purchase #3	$32.48	7.137%	$34.7981	$34.80	$34.80	$34.80
Purchase #4	$133.33	13.337%	$151.1122	$151.11	$151.10	$151.10
Purchase #5	$166.91	7.414%	$179.2847	$179.28	$179.30	$179.30
Purchase #6	$32.55	13.283%	$36.8736	$36.87	$36.85	$36.90
Purchase #7	$166.36	11.730%	$185.874	$185.87	$185.85	$185.90
7 purchase totals =	$996.23		$1,090.5274	$1,090.52	$1,090.50	$1,090.50