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	$173.95	6.253%	$184.8271	$184.83	$184.85	$184.80
Purchase #2	$130.25	10.166%	$143.4912	$143.49	$143.50	$143.50
Purchase #3	$200.77	9.547%	$219.9375	$219.94	$219.95	$219.90
Purchase #4	$89.46	12.829%	$100.9368	$100.94	$100.95	$100.90
Purchase #5	$12.82	7.755%	$13.8142	$13.81	$13.80	$13.80
Purchase #6	$83.73	13.199%	$94.7815	$94.78	$94.80	$94.80
Purchase #7	$89.39	13.434%	$101.3987	$101.40	$101.40	$101.40
7 purchase totals =	$780.37		$859.1870	$859.19	$859.25	$859.10