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	$10.72	13.230%	$12.1383	$12.14	$12.15	$12.10
Purchase #2	$203.30	6.709%	$216.9394	$216.94	$216.95	$216.90
Purchase #3	$248.99	13.253%	$281.9886	$281.99	$282.00	$282.00
Purchase #4	$206.29	8.258%	$223.3254	$223.33	$223.35	$223.30
Purchase #5	$131.88	3.331%	$136.2729	$136.27	$136.25	$136.30
Purchase #6	$214.64	4.155%	$223.5583	$223.56	$223.55	$223.60
Purchase #7	$39.53	7.403%	$42.4564	$42.46	$42.45	$42.50
7 purchase totals =	$1,055.35		$1,136.6793	$1,136.69	$1,136.70	$1,136.70