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	$166.26	11.824%	$185.9186	$185.92	$185.90	$185.90
Purchase #2	$82.71	9.380%	$90.4682	$90.47	$90.45	$90.50
Purchase #3	$212.66	9.776%	$233.4496	$233.45	$233.45	$233.40
Purchase #4	$55.99	13.292%	$63.4322	$63.43	$63.45	$63.40
Purchase #5	$93.33	8.307%	$101.0829	$101.08	$101.10	$101.10
Purchase #6	$18.54	10.612%	$20.5075	$20.51	$20.50	$20.50
Purchase #7	$183.76	7.769%	$198.0363	$198.04	$198.05	$198.00
7 purchase totals =	$813.25		$892.8953	$892.90	$892.90	$892.80