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	$189.40	9.571%	$207.5275	$207.53	$207.55	$207.50
Purchase #2	$95.30	8.438%	$103.3414	$103.34	$103.35	$103.30
Purchase #3	$140.63	5.578%	$148.4743	$148.47	$148.45	$148.50
Purchase #4	$153.84	10.667%	$170.2501	$170.25	$170.25	$170.30
Purchase #5	$10.60	9.358%	$11.5919	$11.59	$11.60	$11.60
Purchase #6	$114.72	12.351%	$128.8891	$128.89	$128.90	$128.90
Purchase #7	$104.91	4.377%	$109.5019	$109.50	$109.50	$109.50
7 purchase totals =	$809.40		$879.5762	$879.57	$879.60	$879.60