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	$163.56	4.745%	$171.3209	$171.32	$171.30	$171.30
Purchase #2	$185.47	9.565%	$203.2102	$203.21	$203.20	$203.20
Purchase #3	$18.78	7.600%	$20.2073	$20.21	$20.20	$20.20
Purchase #4	$55.46	10.196%	$61.1147	$61.11	$61.10	$61.10
Purchase #5	$99.91	12.295%	$112.1939	$112.19	$112.20	$112.20
Purchase #6	$92.80	3.373%	$95.9301	$95.93	$95.95	$95.90
Purchase #7	$19.27	11.499%	$21.4859	$21.49	$21.50	$21.50
7 purchase totals =	$635.25		$685.4630	$685.46	$685.45	$685.40