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	$57.29	4.256%	$59.7283	$59.73	$59.75	$59.70
Purchase #2	$131.95	4.235%	$137.5381	$137.54	$137.55	$137.50
Purchase #3	$105.75	3.508%	$109.4597	$109.46	$109.45	$109.50
Purchase #4	$166.49	7.773%	$179.4313	$179.43	$179.45	$179.40
Purchase #5	$166.47	13.863%	$189.5477	$189.55	$189.55	$189.50
Purchase #6	$96.97	12.128%	$108.7305	$108.73	$108.75	$108.70
Purchase #7	$8.44	7.825%	$9.1004	$9.10	$9.10	$9.10
7 purchase totals =	$733.36		$793.5360	$793.54	$793.60	$793.40