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	$9.69	4.120%	$10.0892	$10.09	$10.10	$10.10
Purchase #2	$158.76	6.341%	$168.827	$168.83	$168.85	$168.80
Purchase #3	$233.83	13.113%	$264.4921	$264.49	$264.50	$264.50
Purchase #4	$154.69	11.129%	$171.9055	$171.91	$171.90	$171.90
Purchase #5	$139.79	5.162%	$147.006	$147.01	$147.00	$147.00
Purchase #6	$45.37	11.624%	$50.6438	$50.64	$50.65	$50.60
Purchase #7	$189.26	10.727%	$209.5619	$209.56	$209.55	$209.60
7 purchase totals =	$931.39		$1,022.5255	$1,022.53	$1,022.55	$1,022.50