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	$54.43	8.618%	$59.1208	$59.12	$59.10	$59.10
Purchase #2	$225.53	11.211%	$250.8142	$250.81	$250.80	$250.80
Purchase #3	$137.90	5.226%	$145.1067	$145.11	$145.10	$145.10
Purchase #4	$207.45	7.826%	$223.685	$223.69	$223.70	$223.70
Purchase #5	$89.42	12.410%	$100.517	$100.52	$100.50	$100.50
Purchase #6	$178.81	6.153%	$189.8122	$189.81	$189.80	$189.80
Purchase #7	$93.80	10.209%	$103.376	$103.38	$103.40	$103.40
7 purchase totals =	$987.34		$1,072.4319	$1,072.44	$1,072.40	$1,072.40