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	$76.92	8.510%	$83.4659	$83.47	$83.45	$83.50
Purchase #2	$77.27	6.313%	$82.1481	$82.15	$82.15	$82.10
Purchase #3	$27.85	10.436%	$30.7564	$30.76	$30.75	$30.80
Purchase #4	$137.36	3.770%	$142.5385	$142.54	$142.55	$142.50
Purchase #5	$108.83	5.777%	$115.1171	$115.12	$115.10	$115.10
Purchase #6	$8.32	4.650%	$8.7069	$8.71	$8.70	$8.70
Purchase #7	$116.70	12.644%	$131.4555	$131.46	$131.45	$131.50
7 purchase totals =	$553.25		$594.1884	$594.21	$594.15	$594.20