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	$181.27	12.551%	$204.0212	$204.02	$204.00	$204.00
Purchase #2	$25.54	12.590%	$28.7555	$28.76	$28.75	$28.80
Purchase #3	$100.57	9.168%	$109.7903	$109.79	$109.80	$109.80
Purchase #4	$223.61	3.288%	$230.9623	$230.96	$230.95	$231.00
Purchase #5	$163.70	4.679%	$171.3595	$171.36	$171.35	$171.40
Purchase #6	$56.88	5.361%	$59.9293	$59.93	$59.95	$59.90
Purchase #7	$117.99	4.593%	$123.4093	$123.41	$123.40	$123.40
7 purchase totals =	$869.56		$928.2274	$928.23	$928.20	$928.30