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	$93.51	6.492%	$99.5807	$99.58	$99.60	$99.60
Purchase #2	$6.60	3.764%	$6.8484	$6.85	$6.85	$6.80
Purchase #3	$33.59	6.654%	$35.8251	$35.83	$35.85	$35.80
Purchase #4	$18.56	12.247%	$20.833	$20.83	$20.85	$20.80
Purchase #5	$130.65	3.428%	$135.1287	$135.13	$135.15	$135.10
Purchase #6	$173.62	9.370%	$189.8882	$189.89	$189.90	$189.90
Purchase #7	$31.52	6.110%	$33.4459	$33.45	$33.45	$33.40
7 purchase totals =	$488.05		$521.5500	$521.56	$521.65	$521.40