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	$6.75	5.497%	$7.121	$7.12	$7.10	$7.10
Purchase #2	$47.62	9.463%	$52.1263	$52.13	$52.15	$52.10
Purchase #3	$104.29	11.715%	$116.5076	$116.51	$116.50	$116.50
Purchase #4	$119.81	11.215%	$133.2467	$133.25	$133.25	$133.20
Purchase #5	$113.34	6.697%	$120.9304	$120.93	$120.95	$120.90
Purchase #6	$33.35	7.361%	$35.8049	$35.80	$35.80	$35.80
Purchase #7	$61.79	7.766%	$66.5886	$66.59	$66.60	$66.60
7 purchase totals =	$486.95		$532.3255	$532.33	$532.35	$532.20