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	$32.97	6.784%	$35.2067	$35.21	$35.20	$35.20
Purchase #2	$103.57	8.825%	$112.7101	$112.71	$112.70	$112.70
Purchase #3	$95.63	3.321%	$98.8059	$98.81	$98.80	$98.80
Purchase #4	$213.42	8.525%	$231.6141	$231.61	$231.60	$231.60
Purchase #5	$53.69	11.529%	$59.8799	$59.88	$59.90	$59.90
Purchase #6	$59.82	13.561%	$67.9322	$67.93	$67.95	$67.90
Purchase #7	$247.38	12.445%	$278.1664	$278.17	$278.15	$278.20
7 purchase totals =	$806.48		$884.3153	$884.32	$884.30	$884.30