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	$29.92	11.312%	$33.3046	$33.30	$33.30	$33.30
Purchase #2	$184.75	6.305%	$196.3985	$196.40	$196.40	$196.40
Purchase #3	$219.35	12.229%	$246.1743	$246.17	$246.15	$246.20
Purchase #4	$50.27	8.422%	$54.5037	$54.50	$54.50	$54.50
Purchase #5	$87.43	13.600%	$99.3205	$99.32	$99.30	$99.30
Purchase #6	$98.99	9.257%	$108.1535	$108.15	$108.15	$108.20
Purchase #7	$179.35	6.203%	$190.4751	$190.48	$190.50	$190.50
7 purchase totals =	$850.06		$928.3302	$928.32	$928.30	$928.40