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	$143.26	11.610%	$159.8925	$159.89	$159.90	$159.90
Purchase #2	$102.47	3.251%	$105.8013	$105.80	$105.80	$105.80
Purchase #3	$47.33	13.812%	$53.8672	$53.87	$53.85	$53.90
Purchase #4	$33.98	5.687%	$35.9124	$35.91	$35.90	$35.90
Purchase #5	$97.38	5.777%	$103.0056	$103.01	$103.00	$103.00
Purchase #6	$86.80	9.555%	$95.0937	$95.09	$95.10	$95.10
Purchase #7	$41.97	7.802%	$45.2445	$45.24	$45.25	$45.20
7 purchase totals =	$553.19		$598.8172	$598.81	$598.80	$598.80