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	$75.27	13.200%	$85.2056	$85.21	$85.20	$85.20
Purchase #2	$101.70	3.791%	$105.5554	$105.56	$105.55	$105.60
Purchase #3	$123.72	11.154%	$137.5197	$137.52	$137.50	$137.50
Purchase #4	$80.34	9.489%	$87.9635	$87.96	$87.95	$88.00
Purchase #5	$124.71	6.520%	$132.8411	$132.84	$132.85	$132.80
Purchase #6	$53.39	12.125%	$59.8635	$59.86	$59.85	$59.90
Purchase #7	$190.29	5.303%	$200.3811	$200.38	$200.40	$200.40
7 purchase totals =	$749.42		$809.3299	$809.33	$809.30	$809.40