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	$76.34	11.854%	$85.3893	$85.39	$85.40	$85.40
Purchase #2	$84.63	6.244%	$89.9143	$89.91	$89.90	$89.90
Purchase #3	$179.48	8.590%	$194.8973	$194.90	$194.90	$194.90
Purchase #4	$123.79	10.367%	$136.6233	$136.62	$136.60	$136.60
Purchase #5	$250.97	4.169%	$261.4329	$261.43	$261.45	$261.40
Purchase #6	$11.97	5.317%	$12.6064	$12.61	$12.60	$12.60
Purchase #7	$133.49	8.729%	$145.1423	$145.14	$145.15	$145.10
7 purchase totals =	$860.67		$926.0058	$926.00	$926.00	$925.90