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	$90.51	3.746%	$93.9005	$93.90	$93.90	$93.90
Purchase #2	$103.28	3.533%	$106.9289	$106.93	$106.95	$106.90
Purchase #3	$100.65	3.224%	$103.895	$103.90	$103.90	$103.90
Purchase #4	$29.96	7.718%	$32.2723	$32.27	$32.25	$32.30
Purchase #5	$77.59	4.511%	$81.0901	$81.09	$81.10	$81.10
Purchase #6	$144.52	7.304%	$155.0757	$155.08	$155.10	$155.10
Purchase #7	$88.76	12.465%	$99.8239	$99.82	$99.80	$99.80
7 purchase totals =	$635.27		$672.9864	$672.99	$673.00	$673.00