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	$128.48	9.304%	$140.4338	$140.43	$140.45	$140.40
Purchase #2	$34.63	7.667%	$37.2851	$37.29	$37.30	$37.30
Purchase #3	$169.52	12.510%	$190.727	$190.73	$190.75	$190.70
Purchase #4	$179.76	9.496%	$196.83	$196.83	$196.85	$196.80
Purchase #5	$106.55	10.126%	$117.3393	$117.34	$117.35	$117.30
Purchase #6	$223.44	12.177%	$250.6483	$250.65	$250.65	$250.60
Purchase #7	$155.45	5.701%	$164.3122	$164.31	$164.30	$164.30
7 purchase totals =	$997.83		$1,097.5757	$1,097.58	$1,097.65	$1,097.40