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	$25.46	5.103%	$26.7592	$26.76	$26.75	$26.80
Purchase #2	$85.54	4.107%	$89.0531	$89.05	$89.05	$89.10
Purchase #3	$235.40	13.192%	$266.454	$266.45	$266.45	$266.50
Purchase #4	$233.83	13.430%	$265.2334	$265.23	$265.25	$265.20
Purchase #5	$196.60	12.866%	$221.8946	$221.89	$221.90	$221.90
Purchase #6	$148.48	7.181%	$159.1423	$159.14	$159.15	$159.10
Purchase #7	$12.34	3.679%	$12.794	$12.79	$12.80	$12.80
7 purchase totals =	$937.65		$1,041.3306	$1,041.31	$1,041.35	$1,041.40