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	$25.33	7.182%	$27.1492	$27.15	$27.15	$27.10
Purchase #2	$56.39	5.840%	$59.6832	$59.68	$59.70	$59.70
Purchase #3	$78.76	11.833%	$88.0797	$88.08	$88.10	$88.10
Purchase #4	$221.70	13.578%	$251.8024	$251.80	$251.80	$251.80
Purchase #5	$128.55	11.512%	$143.3487	$143.35	$143.35	$143.30
Purchase #6	$96.25	4.288%	$100.3772	$100.38	$100.40	$100.40
Purchase #7	$224.76	12.619%	$253.1225	$253.12	$253.10	$253.10
7 purchase totals =	$831.74		$923.5629	$923.56	$923.60	$923.50