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	$101.98	4.766%	$106.8404	$106.84	$106.85	$106.80
Purchase #2	$37.98	5.508%	$40.0719	$40.07	$40.05	$40.10
Purchase #3	$67.69	13.149%	$76.5906	$76.59	$76.60	$76.60
Purchase #4	$65.94	7.698%	$71.0161	$71.02	$71.00	$71.00
Purchase #5	$7.46	11.712%	$8.3337	$8.33	$8.35	$8.30
Purchase #6	$242.71	4.670%	$254.0446	$254.04	$254.05	$254.00
Purchase #7	$116.77	8.816%	$127.0644	$127.06	$127.05	$127.10
7 purchase totals =	$640.53		$683.9617	$683.95	$683.95	$683.90