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	$83.65	9.338%	$91.4612	$91.46	$91.45	$91.50
Purchase #2	$174.86	9.676%	$191.7795	$191.78	$191.80	$191.80
Purchase #3	$28.31	11.600%	$31.594	$31.59	$31.60	$31.60
Purchase #4	$162.42	10.723%	$179.8363	$179.84	$179.85	$179.80
Purchase #5	$89.84	10.858%	$99.5948	$99.59	$99.60	$99.60
Purchase #6	$36.26	8.110%	$39.2007	$39.20	$39.20	$39.20
Purchase #7	$65.81	4.573%	$68.8195	$68.82	$68.80	$68.80
7 purchase totals =	$641.15		$702.2860	$702.28	$702.30	$702.30