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	$139.64	12.126%	$156.5727	$156.57	$156.55	$156.60
Purchase #2	$230.85	8.304%	$250.0198	$250.02	$250.00	$250.00
Purchase #3	$46.84	13.378%	$53.1063	$53.11	$53.10	$53.10
Purchase #4	$90.53	4.501%	$94.6048	$94.60	$94.60	$94.60
Purchase #5	$169.60	11.655%	$189.3669	$189.37	$189.35	$189.40
Purchase #6	$59.47	11.108%	$66.0759	$66.08	$66.10	$66.10
Purchase #7	$97.95	7.325%	$105.1248	$105.12	$105.10	$105.10
7 purchase totals =	$834.88		$914.8712	$914.87	$914.80	$914.90