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	$16.33	13.168%	$18.4803	$18.48	$18.50	$18.50
Purchase #2	$35.93	9.334%	$39.2837	$39.28	$39.30	$39.30
Purchase #3	$50.31	5.812%	$53.234	$53.23	$53.25	$53.20
Purchase #4	$172.57	12.671%	$194.4363	$194.44	$194.45	$194.40
Purchase #5	$94.66	9.409%	$103.5666	$103.57	$103.55	$103.60
Purchase #6	$72.49	8.637%	$78.751	$78.75	$78.75	$78.80
Purchase #7	$54.83	12.365%	$61.6097	$61.61	$61.60	$61.60
7 purchase totals =	$497.12		$549.3616	$549.36	$549.40	$549.40