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	$76.58	4.653%	$80.1433	$80.14	$80.15	$80.10
Purchase #2	$250.76	13.851%	$285.4928	$285.49	$285.50	$285.50
Purchase #3	$92.38	9.746%	$101.3834	$101.38	$101.40	$101.40
Purchase #4	$195.69	11.201%	$217.6092	$217.61	$217.60	$217.60
Purchase #5	$126.61	4.604%	$132.4391	$132.44	$132.45	$132.40
Purchase #6	$164.72	10.488%	$181.9958	$182.00	$182.00	$182.00
Purchase #7	$120.71	9.399%	$132.0555	$132.06	$132.05	$132.10
7 purchase totals =	$1,027.45		$1,131.1191	$1,131.12	$1,131.15	$1,131.10