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	$60.81	11.266%	$67.6609	$67.66	$67.65	$67.70
Purchase #2	$145.31	9.650%	$159.3324	$159.33	$159.35	$159.30
Purchase #3	$156.50	8.700%	$170.1155	$170.12	$170.10	$170.10
Purchase #4	$37.40	8.578%	$40.6082	$40.61	$40.60	$40.60
Purchase #5	$43.48	11.874%	$48.6428	$48.64	$48.65	$48.60
Purchase #6	$11.48	8.608%	$12.4682	$12.47	$12.45	$12.50
Purchase #7	$234.80	4.666%	$245.7558	$245.76	$245.75	$245.80
7 purchase totals =	$689.78		$744.5838	$744.59	$744.55	$744.60