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	$105.74	7.298%	$113.4569	$113.46	$113.45	$113.50
Purchase #2	$213.81	13.326%	$242.3023	$242.30	$242.30	$242.30
Purchase #3	$90.92	9.709%	$99.7474	$99.75	$99.75	$99.70
Purchase #4	$13.61	11.869%	$15.2254	$15.23	$15.25	$15.20
Purchase #5	$34.65	6.178%	$36.7907	$36.79	$36.80	$36.80
Purchase #6	$89.35	12.694%	$100.6921	$100.69	$100.70	$100.70
Purchase #7	$49.86	11.778%	$55.7325	$55.73	$55.75	$55.70
7 purchase totals =	$597.94		$663.9473	$663.95	$664.00	$663.90