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	$89.90	5.455%	$94.804	$94.80	$94.80	$94.80
Purchase #2	$198.40	12.642%	$223.4817	$223.48	$223.50	$223.50
Purchase #3	$143.78	10.311%	$158.6052	$158.61	$158.60	$158.60
Purchase #4	$179.89	6.585%	$191.7358	$191.74	$191.75	$191.70
Purchase #5	$222.80	11.619%	$248.6871	$248.69	$248.70	$248.70
Purchase #6	$110.73	4.777%	$116.0196	$116.02	$116.00	$116.00
Purchase #7	$81.82	13.556%	$92.9115	$92.91	$92.90	$92.90
7 purchase totals =	$1,027.32		$1,126.2449	$1,126.25	$1,126.25	$1,126.20