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	$229.38	8.375%	$248.5906	$248.59	$248.60	$248.60
Purchase #2	$123.77	3.709%	$128.3606	$128.36	$128.35	$128.40
Purchase #3	$145.59	13.427%	$165.1384	$165.14	$165.15	$165.10
Purchase #4	$154.76	10.123%	$170.4264	$170.43	$170.45	$170.40
Purchase #5	$209.34	6.240%	$222.4028	$222.40	$222.40	$222.40
Purchase #6	$138.48	11.404%	$154.2723	$154.27	$154.25	$154.30
Purchase #7	$32.49	9.757%	$35.66	$35.66	$35.65	$35.70
7 purchase totals =	$1,033.81		$1,124.8511	$1,124.85	$1,124.85	$1,124.90