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	$158.80	7.684%	$171.0022	$171.00	$171.00	$171.00
Purchase #2	$148.64	12.467%	$167.1709	$167.17	$167.15	$167.20
Purchase #3	$123.50	12.616%	$139.0808	$139.08	$139.10	$139.10
Purchase #4	$65.73	10.793%	$72.8242	$72.82	$72.80	$72.80
Purchase #5	$64.63	11.138%	$71.8285	$71.83	$71.85	$71.80
Purchase #6	$250.26	10.754%	$277.173	$277.17	$277.15	$277.20
Purchase #7	$106.81	9.578%	$117.0403	$117.04	$117.05	$117.00
7 purchase totals =	$918.37		$1,016.1199	$1,016.11	$1,016.10	$1,016.10