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	$32.63	8.734%	$35.4799	$35.48	$35.50	$35.50
Purchase #2	$170.72	12.658%	$192.3297	$192.33	$192.35	$192.30
Purchase #3	$130.97	9.367%	$143.238	$143.24	$143.25	$143.20
Purchase #4	$5.86	7.706%	$6.3116	$6.31	$6.30	$6.30
Purchase #5	$81.31	12.668%	$91.6104	$91.61	$91.60	$91.60
Purchase #6	$88.33	13.434%	$100.1963	$100.20	$100.20	$100.20
Purchase #7	$71.71	12.808%	$80.8946	$80.89	$80.90	$80.90
7 purchase totals =	$581.53		$650.0605	$650.06	$650.10	$650.00