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	$27.79	8.575%	$30.173	$30.17	$30.15	$30.20
Purchase #2	$112.75	9.369%	$123.3135	$123.31	$123.30	$123.30
Purchase #3	$139.60	8.465%	$151.4171	$151.42	$151.40	$151.40
Purchase #4	$79.81	13.820%	$90.8397	$90.84	$90.85	$90.80
Purchase #5	$193.41	5.534%	$204.1133	$204.11	$204.10	$204.10
Purchase #6	$123.39	13.248%	$139.7367	$139.74	$139.75	$139.70
Purchase #7	$84.71	7.376%	$90.9582	$90.96	$90.95	$91.00
7 purchase totals =	$761.46		$830.5515	$830.55	$830.50	$830.50