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	$169.26	4.506%	$176.8869	$176.89	$176.90	$176.90
Purchase #2	$195.76	12.164%	$219.5722	$219.57	$219.55	$219.60
Purchase #3	$139.30	7.596%	$149.8812	$149.88	$149.90	$149.90
Purchase #4	$131.88	9.636%	$144.588	$144.59	$144.60	$144.60
Purchase #5	$34.93	10.119%	$38.4646	$38.46	$38.45	$38.50
Purchase #6	$74.78	8.196%	$80.909	$80.91	$80.90	$80.90
Purchase #7	$35.69	6.478%	$38.002	$38.00	$38.00	$38.00
7 purchase totals =	$781.60		$848.3039	$848.30	$848.30	$848.40