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	$33.99	10.106%	$37.425	$37.43	$37.45	$37.40
Purchase #2	$127.89	7.817%	$137.8872	$137.89	$137.90	$137.90
Purchase #3	$247.30	12.860%	$279.1028	$279.10	$279.10	$279.10
Purchase #4	$240.35	3.847%	$249.5963	$249.60	$249.60	$249.60
Purchase #5	$108.95	5.334%	$114.7614	$114.76	$114.75	$114.80
Purchase #6	$134.88	12.260%	$151.4163	$151.42	$151.40	$151.40
Purchase #7	$35.70	4.364%	$37.2579	$37.26	$37.25	$37.30
7 purchase totals =	$929.06		$1,007.4469	$1,007.46	$1,007.45	$1,007.50