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	$133.46	12.834%	$150.5883	$150.59	$150.60	$150.60
Purchase #2	$118.37	11.369%	$131.8275	$131.83	$131.85	$131.80
Purchase #3	$99.74	6.763%	$106.4854	$106.49	$106.50	$106.50
Purchase #4	$174.89	4.550%	$182.8475	$182.85	$182.85	$182.80
Purchase #5	$50.80	4.669%	$53.1719	$53.17	$53.15	$53.20
Purchase #6	$29.63	4.152%	$30.8602	$30.86	$30.85	$30.90
Purchase #7	$217.27	9.294%	$237.4631	$237.46	$237.45	$237.50
7 purchase totals =	$824.16		$893.2439	$893.25	$893.25	$893.30