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	$233.77	10.657%	$258.6829	$258.68	$258.70	$258.70
Purchase #2	$82.27	13.797%	$93.6208	$93.62	$93.60	$93.60
Purchase #3	$150.59	7.140%	$161.3421	$161.34	$161.35	$161.30
Purchase #4	$81.77	9.323%	$89.3934	$89.39	$89.40	$89.40
Purchase #5	$157.48	9.682%	$172.7272	$172.73	$172.75	$172.70
Purchase #6	$133.54	7.375%	$143.3886	$143.39	$143.40	$143.40
Purchase #7	$80.34	4.161%	$83.6829	$83.68	$83.70	$83.70
7 purchase totals =	$919.76		$1,002.8379	$1,002.83	$1,002.90	$1,002.80