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	$29.82	8.470%	$32.3458	$32.35	$32.35	$32.30
Purchase #2	$23.85	3.468%	$24.6771	$24.68	$24.70	$24.70
Purchase #3	$126.60	11.267%	$140.864	$140.86	$140.85	$140.90
Purchase #4	$37.29	12.616%	$41.9945	$41.99	$42.00	$42.00
Purchase #5	$237.88	9.556%	$260.6118	$260.61	$260.60	$260.60
Purchase #6	$86.51	5.740%	$91.4757	$91.48	$91.50	$91.50
Purchase #7	$165.49	5.439%	$174.491	$174.49	$174.50	$174.50
7 purchase totals =	$707.44		$766.4599	$766.46	$766.50	$766.50