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	$143.42	7.450%	$154.1048	$154.10	$154.10	$154.10
Purchase #2	$123.36	8.816%	$134.2354	$134.24	$134.25	$134.20
Purchase #3	$188.72	6.138%	$200.3036	$200.30	$200.30	$200.30
Purchase #4	$21.69	9.787%	$23.8128	$23.81	$23.80	$23.80
Purchase #5	$111.47	4.117%	$116.0592	$116.06	$116.05	$116.10
Purchase #6	$144.60	12.415%	$162.5521	$162.55	$162.55	$162.60
Purchase #7	$203.67	4.497%	$212.829	$212.83	$212.85	$212.80
7 purchase totals =	$936.93		$1,003.8969	$1,003.89	$1,003.90	$1,003.90