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	$51.59	6.627%	$55.0089	$55.01	$55.00	$55.00
Purchase #2	$50.63	13.197%	$57.3116	$57.31	$57.30	$57.30
Purchase #3	$88.29	12.786%	$99.5788	$99.58	$99.60	$99.60
Purchase #4	$35.84	5.510%	$37.8148	$37.81	$37.80	$37.80
Purchase #5	$92.44	12.311%	$103.8203	$103.82	$103.80	$103.80
Purchase #6	$171.57	9.853%	$188.4748	$188.47	$188.45	$188.50
Purchase #7	$152.80	12.530%	$171.9458	$171.95	$171.95	$171.90
7 purchase totals =	$643.16		$713.9550	$713.95	$713.90	$713.90