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	$25.37	6.541%	$27.0295	$27.03	$27.05	$27.00
Purchase #2	$96.37	9.191%	$105.2274	$105.23	$105.25	$105.20
Purchase #3	$94.52	12.458%	$106.2953	$106.30	$106.30	$106.30
Purchase #4	$110.66	11.660%	$123.563	$123.56	$123.55	$123.60
Purchase #5	$139.71	9.553%	$153.0565	$153.06	$153.05	$153.10
Purchase #6	$155.85	7.317%	$167.2535	$167.25	$167.25	$167.30
Purchase #7	$232.50	11.746%	$259.8095	$259.81	$259.80	$259.80
7 purchase totals =	$854.98		$942.2347	$942.24	$942.25	$942.30