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	$103.57	5.640%	$109.4113	$109.41	$109.40	$109.40
Purchase #2	$17.34	11.368%	$19.3112	$19.31	$19.30	$19.30
Purchase #3	$113.80	12.698%	$128.2503	$128.25	$128.25	$128.30
Purchase #4	$53.84	7.328%	$57.7854	$57.79	$57.80	$57.80
Purchase #5	$146.39	7.156%	$156.8657	$156.87	$156.85	$156.90
Purchase #6	$182.54	3.843%	$189.555	$189.56	$189.55	$189.60
Purchase #7	$117.82	6.211%	$125.1378	$125.14	$125.15	$125.10
7 purchase totals =	$735.30		$786.3167	$786.33	$786.30	$786.40