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	$155.85	5.529%	$164.4669	$164.47	$164.45	$164.50
Purchase #2	$188.81	11.814%	$211.116	$211.12	$211.10	$211.10
Purchase #3	$59.30	12.740%	$66.8548	$66.85	$66.85	$66.90
Purchase #4	$103.81	7.729%	$111.8335	$111.83	$111.85	$111.80
Purchase #5	$170.33	8.591%	$184.9631	$184.96	$184.95	$185.00
Purchase #6	$85.92	10.613%	$95.0387	$95.04	$95.05	$95.00
Purchase #7	$124.70	10.499%	$137.7923	$137.79	$137.80	$137.80
7 purchase totals =	$888.72		$972.0653	$972.06	$972.05	$972.10