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	$89.76	6.776%	$95.8421	$95.84	$95.85	$95.80
Purchase #2	$148.54	6.433%	$158.0956	$158.10	$158.10	$158.10
Purchase #3	$36.59	9.133%	$39.9318	$39.93	$39.95	$39.90
Purchase #4	$79.92	13.496%	$90.706	$90.71	$90.70	$90.70
Purchase #5	$144.56	8.419%	$156.7305	$156.73	$156.75	$156.70
Purchase #6	$136.40	12.157%	$152.9821	$152.98	$153.00	$153.00
Purchase #7	$136.69	6.468%	$145.5311	$145.53	$145.55	$145.50
7 purchase totals =	$772.46		$839.8192	$839.82	$839.90	$839.70