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	$250.91	6.657%	$267.6131	$267.61	$267.60	$267.60
Purchase #2	$24.66	3.324%	$25.4797	$25.48	$25.50	$25.50
Purchase #3	$52.47	11.571%	$58.5413	$58.54	$58.55	$58.50
Purchase #4	$222.75	12.248%	$250.0324	$250.03	$250.05	$250.00
Purchase #5	$18.80	7.794%	$20.2653	$20.27	$20.25	$20.30
Purchase #6	$205.55	11.135%	$228.438	$228.44	$228.45	$228.40
Purchase #7	$200.71	7.563%	$215.8897	$215.89	$215.90	$215.90
7 purchase totals =	$975.85		$1,066.2595	$1,066.26	$1,066.30	$1,066.20