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	$39.72	7.703%	$42.7796	$42.78	$42.80	$42.80
Purchase #2	$220.36	13.838%	$250.8534	$250.85	$250.85	$250.90
Purchase #3	$111.82	12.143%	$125.3983	$125.40	$125.40	$125.40
Purchase #4	$232.68	11.563%	$259.5848	$259.58	$259.60	$259.60
Purchase #5	$106.92	10.112%	$117.7318	$117.73	$117.75	$117.70
Purchase #6	$96.32	9.443%	$105.4155	$105.42	$105.40	$105.40
Purchase #7	$96.71	10.863%	$107.2156	$107.22	$107.20	$107.20
7 purchase totals =	$904.53		$1,008.9790	$1,008.98	$1,009.00	$1,009.00