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	$180.87	4.668%	$189.313	$189.31	$189.30	$189.30
Purchase #2	$176.50	11.273%	$196.3968	$196.40	$196.40	$196.40
Purchase #3	$45.82	11.774%	$51.2148	$51.21	$51.20	$51.20
Purchase #4	$94.42	7.338%	$101.3485	$101.35	$101.35	$101.30
Purchase #5	$43.68	5.434%	$46.0536	$46.05	$46.05	$46.10
Purchase #6	$131.82	12.551%	$148.3647	$148.36	$148.35	$148.40
Purchase #7	$186.35	13.374%	$211.2724	$211.27	$211.25	$211.30
7 purchase totals =	$859.46		$943.9638	$943.95	$943.90	$944.00