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	$34.32	9.157%	$37.4627	$37.46	$37.45	$37.50
Purchase #2	$58.96	5.553%	$62.234	$62.23	$62.25	$62.20
Purchase #3	$147.67	8.163%	$159.7243	$159.72	$159.70	$159.70
Purchase #4	$117.76	11.227%	$130.9809	$130.98	$131.00	$131.00
Purchase #5	$68.25	6.526%	$72.704	$72.70	$72.70	$72.70
Purchase #6	$11.98	9.542%	$13.1231	$13.12	$13.10	$13.10
Purchase #7	$59.74	4.104%	$62.1917	$62.19	$62.20	$62.20
7 purchase totals =	$498.68		$538.4207	$538.40	$538.40	$538.40