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	$131.86	3.715%	$136.7586	$136.76	$136.75	$136.80
Purchase #2	$91.66	10.172%	$100.9837	$100.98	$101.00	$101.00
Purchase #3	$36.48	13.485%	$41.3993	$41.40	$41.40	$41.40
Purchase #4	$202.60	5.544%	$213.8321	$213.83	$213.85	$213.80
Purchase #5	$29.78	8.106%	$32.194	$32.19	$32.20	$32.20
Purchase #6	$101.62	9.621%	$111.3969	$111.40	$111.40	$111.40
Purchase #7	$48.48	9.118%	$52.9004	$52.90	$52.90	$52.90
7 purchase totals =	$642.48		$689.4650	$689.46	$689.50	$689.50