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	$35.98	12.202%	$40.3703	$40.37	$40.35	$40.40
Purchase #2	$85.26	11.845%	$95.359	$95.36	$95.35	$95.40
Purchase #3	$156.88	6.305%	$166.7713	$166.77	$166.75	$166.80
Purchase #4	$57.87	11.371%	$64.4504	$64.45	$64.45	$64.50
Purchase #5	$141.73	12.368%	$159.2592	$159.26	$159.25	$159.30
Purchase #6	$75.65	5.521%	$79.8266	$79.83	$79.85	$79.80
Purchase #7	$89.69	11.368%	$99.886	$99.89	$99.90	$99.90
7 purchase totals =	$643.06		$705.9228	$705.93	$705.90	$706.10