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	$149.84	10.707%	$165.8834	$165.88	$165.90	$165.90
Purchase #2	$91.39	13.324%	$103.5668	$103.57	$103.55	$103.60
Purchase #3	$128.34	12.635%	$144.5558	$144.56	$144.55	$144.60
Purchase #4	$26.36	5.738%	$27.8725	$27.87	$27.85	$27.90
Purchase #5	$123.90	10.520%	$136.9343	$136.93	$136.95	$136.90
Purchase #6	$128.25	13.620%	$145.7177	$145.72	$145.70	$145.70
Purchase #7	$80.78	11.498%	$90.0681	$90.07	$90.05	$90.10
7 purchase totals =	$728.86		$814.5986	$814.60	$814.55	$814.70