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	$104.61	5.204%	$110.0539	$110.05	$110.05	$110.10
Purchase #2	$55.28	7.152%	$59.2336	$59.23	$59.25	$59.20
Purchase #3	$30.52	7.553%	$32.8252	$32.83	$32.85	$32.80
Purchase #4	$81.32	3.187%	$83.9117	$83.91	$83.90	$83.90
Purchase #5	$52.96	13.668%	$60.1986	$60.20	$60.20	$60.20
Purchase #6	$142.94	7.637%	$153.8563	$153.86	$153.85	$153.90
Purchase #7	$18.41	13.742%	$20.9399	$20.94	$20.95	$20.90
7 purchase totals =	$486.04		$521.0192	$521.02	$521.05	$521.00