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	$7.30	6.495%	$7.7741	$7.77	$7.75	$7.80
Purchase #2	$137.45	4.207%	$143.2325	$143.23	$143.25	$143.20
Purchase #3	$45.46	4.538%	$47.523	$47.52	$47.50	$47.50
Purchase #4	$181.85	9.838%	$199.7404	$199.74	$199.75	$199.70
Purchase #5	$91.80	4.465%	$95.8989	$95.90	$95.90	$95.90
Purchase #6	$247.60	12.322%	$278.1093	$278.11	$278.10	$278.10
Purchase #7	$72.37	6.795%	$77.2875	$77.29	$77.30	$77.30
7 purchase totals =	$783.83		$849.5657	$849.56	$849.55	$849.50