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	$59.89	3.210%	$61.8125	$61.81	$61.80	$61.80
Purchase #2	$89.45	4.425%	$93.4082	$93.41	$93.40	$93.40
Purchase #3	$104.33	7.418%	$112.0692	$112.07	$112.05	$112.10
Purchase #4	$66.33	5.655%	$70.081	$70.08	$70.10	$70.10
Purchase #5	$107.32	3.667%	$111.2554	$111.26	$111.25	$111.30
Purchase #6	$117.73	5.526%	$124.2358	$124.24	$124.25	$124.20
Purchase #7	$87.74	11.571%	$97.8924	$97.89	$97.90	$97.90
7 purchase totals =	$632.79		$670.7545	$670.76	$670.75	$670.80