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	$78.90	13.201%	$89.3156	$89.32	$89.30	$89.30
Purchase #2	$159.72	9.576%	$175.0148	$175.01	$175.00	$175.00
Purchase #3	$240.74	4.350%	$251.2122	$251.21	$251.20	$251.20
Purchase #4	$10.47	3.398%	$10.8258	$10.83	$10.85	$10.80
Purchase #5	$202.51	10.306%	$223.3807	$223.38	$223.40	$223.40
Purchase #6	$155.95	7.359%	$167.4264	$167.43	$167.45	$167.40
Purchase #7	$32.54	9.552%	$35.6482	$35.65	$35.65	$35.60
7 purchase totals =	$880.83		$952.8237	$952.83	$952.85	$952.70