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	$90.66	9.776%	$99.5229	$99.52	$99.50	$99.50
Purchase #2	$180.54	5.183%	$189.8974	$189.90	$189.90	$189.90
Purchase #3	$161.98	4.208%	$168.7961	$168.80	$168.80	$168.80
Purchase #4	$25.61	3.250%	$26.4423	$26.44	$26.45	$26.40
Purchase #5	$248.47	11.499%	$277.0416	$277.04	$277.05	$277.00
Purchase #6	$225.98	12.821%	$254.9529	$254.95	$254.95	$255.00
Purchase #7	$31.32	7.271%	$33.5973	$33.60	$33.60	$33.60
7 purchase totals =	$964.56		$1,050.2505	$1,050.25	$1,050.25	$1,050.20