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	$94.58	10.550%	$104.5582	$104.56	$104.55	$104.60
Purchase #2	$151.83	9.244%	$165.8652	$165.87	$165.85	$165.90
Purchase #3	$89.42	5.636%	$94.4597	$94.46	$94.45	$94.50
Purchase #4	$98.71	12.295%	$110.8464	$110.85	$110.85	$110.80
Purchase #5	$82.67	4.107%	$86.0653	$86.07	$86.05	$86.10
Purchase #6	$114.87	13.346%	$130.2006	$130.20	$130.20	$130.20
Purchase #7	$243.25	12.837%	$274.476	$274.48	$274.50	$274.50
7 purchase totals =	$875.33		$966.4714	$966.49	$966.45	$966.60