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	$16.82	7.408%	$18.066	$18.07	$18.05	$18.10
Purchase #2	$65.97	8.815%	$71.7853	$71.79	$71.80	$71.80
Purchase #3	$119.47	9.207%	$130.4696	$130.47	$130.45	$130.50
Purchase #4	$191.34	10.307%	$211.0614	$211.06	$211.05	$211.10
Purchase #5	$20.30	3.128%	$20.935	$20.94	$20.95	$20.90
Purchase #6	$184.31	8.544%	$200.0574	$200.06	$200.05	$200.10
Purchase #7	$81.27	3.152%	$83.8316	$83.83	$83.85	$83.80
7 purchase totals =	$679.48		$736.2063	$736.22	$736.20	$736.30