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	$140.52	7.244%	$150.6993	$150.70	$150.70	$150.70
Purchase #2	$55.61	13.253%	$62.98	$62.98	$63.00	$63.00
Purchase #3	$233.72	9.631%	$256.2296	$256.23	$256.25	$256.20
Purchase #4	$178.52	7.677%	$192.225	$192.23	$192.25	$192.20
Purchase #5	$7.33	12.837%	$8.271	$8.27	$8.25	$8.30
Purchase #6	$141.57	13.264%	$160.3478	$160.35	$160.35	$160.30
Purchase #7	$91.26	10.295%	$100.6552	$100.66	$100.65	$100.70
7 purchase totals =	$848.53		$931.4079	$931.42	$931.45	$931.40