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	$33.77	5.500%	$35.6274	$35.63	$35.65	$35.60
Purchase #2	$134.52	4.227%	$140.2062	$140.21	$140.20	$140.20
Purchase #3	$93.50	5.812%	$98.9342	$98.93	$98.95	$98.90
Purchase #4	$189.85	4.565%	$198.5167	$198.52	$198.50	$198.50
Purchase #5	$92.53	11.457%	$103.1312	$103.13	$103.15	$103.10
Purchase #6	$42.83	6.726%	$45.7107	$45.71	$45.70	$45.70
Purchase #7	$147.81	4.788%	$154.8871	$154.89	$154.90	$154.90
7 purchase totals =	$734.81		$777.0135	$777.02	$777.05	$776.90