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	$51.83	13.687%	$58.924	$58.92	$58.90	$58.90
Purchase #2	$81.28	11.155%	$90.3468	$90.35	$90.35	$90.30
Purchase #3	$196.68	13.206%	$222.6536	$222.65	$222.65	$222.70
Purchase #4	$88.69	3.173%	$91.5041	$91.50	$91.50	$91.50
Purchase #5	$88.61	5.658%	$93.6236	$93.62	$93.60	$93.60
Purchase #6	$120.61	10.143%	$132.8435	$132.84	$132.85	$132.80
Purchase #7	$35.62	11.597%	$39.7509	$39.75	$39.75	$39.80
7 purchase totals =	$663.32		$729.6465	$729.63	$729.60	$729.60