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	$142.50	6.560%	$151.848	$151.85	$151.85	$151.80
Purchase #2	$89.28	4.315%	$93.1324	$93.13	$93.15	$93.10
Purchase #3	$35.99	3.863%	$37.3803	$37.38	$37.40	$37.40
Purchase #4	$54.38	8.646%	$59.0817	$59.08	$59.10	$59.10
Purchase #5	$235.49	5.677%	$248.8588	$248.86	$248.85	$248.90
Purchase #6	$172.91	11.196%	$192.269	$192.27	$192.25	$192.30
Purchase #7	$51.42	13.419%	$58.32	$58.32	$58.30	$58.30
7 purchase totals =	$781.97		$840.8902	$840.89	$840.90	$840.90