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	$80.35	10.251%	$88.5867	$88.59	$88.60	$88.60
Purchase #2	$119.67	9.132%	$130.5983	$130.60	$130.60	$130.60
Purchase #3	$65.33	10.456%	$72.1609	$72.16	$72.15	$72.20
Purchase #4	$210.45	7.833%	$226.9345	$226.93	$226.95	$226.90
Purchase #5	$93.88	11.678%	$104.8433	$104.84	$104.85	$104.80
Purchase #6	$97.52	9.191%	$106.4831	$106.48	$106.50	$106.50
Purchase #7	$143.70	5.417%	$151.4842	$151.48	$151.50	$151.50
7 purchase totals =	$810.90		$881.0910	$881.08	$881.15	$881.10