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	$168.44	6.298%	$179.0484	$179.05	$179.05	$179.00
Purchase #2	$221.42	10.786%	$245.3024	$245.30	$245.30	$245.30
Purchase #3	$119.94	9.728%	$131.6078	$131.61	$131.60	$131.60
Purchase #4	$35.71	13.603%	$40.5676	$40.57	$40.55	$40.60
Purchase #5	$83.82	12.399%	$94.2128	$94.21	$94.20	$94.20
Purchase #6	$118.34	5.225%	$124.5233	$124.52	$124.50	$124.50
Purchase #7	$147.91	4.729%	$154.9047	$154.90	$154.90	$154.90
7 purchase totals =	$895.58		$970.1670	$970.16	$970.10	$970.10