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	$37.50	12.478%	$42.1793	$42.18	$42.20	$42.20
Purchase #2	$103.45	5.170%	$108.7984	$108.80	$108.80	$108.80
Purchase #3	$110.56	11.805%	$123.6116	$123.61	$123.60	$123.60
Purchase #4	$234.52	8.609%	$254.7098	$254.71	$254.70	$254.70
Purchase #5	$203.67	11.577%	$227.2489	$227.25	$227.25	$227.20
Purchase #6	$109.95	4.340%	$114.7218	$114.72	$114.70	$114.70
Purchase #7	$148.55	11.151%	$165.1148	$165.11	$165.10	$165.10
7 purchase totals =	$948.20		$1,036.3846	$1,036.38	$1,036.35	$1,036.30