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	$92.91	5.822%	$98.3192	$98.32	$98.30	$98.30
Purchase #2	$207.57	8.707%	$225.6431	$225.64	$225.65	$225.60
Purchase #3	$243.51	11.436%	$271.3578	$271.36	$271.35	$271.40
Purchase #4	$197.42	7.818%	$212.8543	$212.85	$212.85	$212.90
Purchase #5	$39.77	7.610%	$42.7965	$42.80	$42.80	$42.80
Purchase #6	$52.60	13.550%	$59.7273	$59.73	$59.75	$59.70
Purchase #7	$75.51	9.620%	$82.7741	$82.77	$82.75	$82.80
7 purchase totals =	$909.29		$993.4723	$993.47	$993.45	$993.50