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	$109.57	13.222%	$124.0573	$124.06	$124.05	$124.10
Purchase #2	$171.51	4.527%	$179.2743	$179.27	$179.25	$179.30
Purchase #3	$20.44	7.343%	$21.9409	$21.94	$21.95	$21.90
Purchase #4	$150.39	10.651%	$166.408	$166.41	$166.40	$166.40
Purchase #5	$238.57	6.275%	$253.5403	$253.54	$253.55	$253.50
Purchase #6	$24.76	11.744%	$27.6678	$27.67	$27.65	$27.70
Purchase #7	$110.32	6.314%	$117.2856	$117.29	$117.30	$117.30
7 purchase totals =	$825.56		$890.1742	$890.18	$890.15	$890.20