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	$171.76	9.119%	$187.4228	$187.42	$187.40	$187.40
Purchase #2	$35.46	9.228%	$38.7322	$38.73	$38.75	$38.70
Purchase #3	$156.84	10.131%	$172.7295	$172.73	$172.75	$172.70
Purchase #4	$129.59	7.139%	$138.8414	$138.84	$138.85	$138.80
Purchase #5	$26.25	12.714%	$29.5874	$29.59	$29.60	$29.60
Purchase #6	$246.96	3.791%	$256.3223	$256.32	$256.30	$256.30
Purchase #7	$140.74	13.840%	$160.2184	$160.22	$160.20	$160.20
7 purchase totals =	$907.60		$983.8540	$983.85	$983.85	$983.70