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	$123.84	6.251%	$131.5812	$131.58	$131.60	$131.60
Purchase #2	$156.45	7.148%	$167.633	$167.63	$167.65	$167.60
Purchase #3	$100.64	13.834%	$114.5625	$114.56	$114.55	$114.60
Purchase #4	$58.69	12.440%	$65.991	$65.99	$66.00	$66.00
Purchase #5	$89.84	11.229%	$99.9281	$99.93	$99.95	$99.90
Purchase #6	$40.31	5.708%	$42.6109	$42.61	$42.60	$42.60
Purchase #7	$16.42	11.571%	$18.32	$18.32	$18.30	$18.30
7 purchase totals =	$586.19		$640.6267	$640.62	$640.65	$640.60