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	$204.60	6.121%	$217.1236	$217.12	$217.10	$217.10
Purchase #2	$169.53	12.372%	$190.5043	$190.50	$190.50	$190.50
Purchase #3	$80.72	10.277%	$89.0156	$89.02	$89.00	$89.00
Purchase #4	$88.62	4.431%	$92.5468	$92.55	$92.55	$92.50
Purchase #5	$223.48	7.349%	$239.9035	$239.90	$239.90	$239.90
Purchase #6	$88.64	12.117%	$99.3805	$99.38	$99.40	$99.40
Purchase #7	$24.57	12.184%	$27.5636	$27.56	$27.55	$27.60
7 purchase totals =	$880.16		$956.0379	$956.03	$956.00	$956.00