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	$204.85	3.741%	$212.5134	$212.51	$212.50	$212.50
Purchase #2	$146.60	9.744%	$160.8847	$160.88	$160.90	$160.90
Purchase #3	$189.53	12.686%	$213.5738	$213.57	$213.55	$213.60
Purchase #4	$151.41	8.659%	$164.5206	$164.52	$164.50	$164.50
Purchase #5	$113.42	10.646%	$125.4947	$125.49	$125.50	$125.50
Purchase #6	$80.32	11.525%	$89.5769	$89.58	$89.60	$89.60
Purchase #7	$111.29	6.758%	$118.811	$118.81	$118.80	$118.80
7 purchase totals =	$997.42		$1,085.3751	$1,085.36	$1,085.35	$1,085.40