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	$48.94	11.641%	$54.6371	$54.64	$54.65	$54.60
Purchase #2	$83.36	10.728%	$92.3029	$92.30	$92.30	$92.30
Purchase #3	$162.42	7.784%	$175.0628	$175.06	$175.05	$175.10
Purchase #4	$37.32	13.115%	$42.2145	$42.21	$42.20	$42.20
Purchase #5	$91.32	10.519%	$100.926	$100.93	$100.95	$100.90
Purchase #6	$85.39	12.324%	$95.9135	$95.91	$95.90	$95.90
Purchase #7	$211.79	4.110%	$220.4946	$220.49	$220.50	$220.50
7 purchase totals =	$720.54		$781.5514	$781.54	$781.55	$781.50