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	$153.46	8.119%	$165.9194	$165.92	$165.90	$165.90
Purchase #2	$35.50	13.125%	$40.1594	$40.16	$40.15	$40.20
Purchase #3	$52.87	12.526%	$59.4925	$59.49	$59.50	$59.50
Purchase #4	$240.89	9.361%	$263.4397	$263.44	$263.45	$263.40
Purchase #5	$26.50	13.166%	$29.989	$29.99	$30.00	$30.00
Purchase #6	$128.58	12.314%	$144.4133	$144.41	$144.40	$144.40
Purchase #7	$80.81	10.736%	$89.4858	$89.49	$89.50	$89.50
7 purchase totals =	$718.61		$792.8991	$792.90	$792.90	$792.90