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	$81.35	11.198%	$90.4596	$90.46	$90.45	$90.50
Purchase #2	$129.54	11.486%	$144.419	$144.42	$144.40	$144.40
Purchase #3	$232.69	5.331%	$245.0947	$245.09	$245.10	$245.10
Purchase #4	$203.46	10.763%	$225.3584	$225.36	$225.35	$225.40
Purchase #5	$99.30	11.229%	$110.4504	$110.45	$110.45	$110.50
Purchase #6	$98.37	12.140%	$110.3121	$110.31	$110.30	$110.30
Purchase #7	$86.49	8.195%	$93.5779	$93.58	$93.60	$93.60
7 purchase totals =	$931.20		$1,019.6721	$1,019.67	$1,019.65	$1,019.80