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	$20.25	9.349%	$22.1432	$22.14	$22.15	$22.10
Purchase #2	$159.76	5.586%	$168.6842	$168.68	$168.70	$168.70
Purchase #3	$33.28	7.293%	$35.7071	$35.71	$35.70	$35.70
Purchase #4	$106.45	4.474%	$111.2126	$111.21	$111.20	$111.20
Purchase #5	$146.53	12.576%	$164.9576	$164.96	$164.95	$165.00
Purchase #6	$98.69	12.531%	$111.0568	$111.06	$111.05	$111.10
Purchase #7	$242.87	6.355%	$258.3044	$258.30	$258.30	$258.30
7 purchase totals =	$807.83		$872.0659	$872.06	$872.05	$872.10