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	$232.39	4.317%	$242.4223	$242.42	$242.40	$242.40
Purchase #2	$104.83	7.215%	$112.3935	$112.39	$112.40	$112.40
Purchase #3	$245.60	10.800%	$272.1248	$272.12	$272.10	$272.10
Purchase #4	$17.32	5.774%	$18.3201	$18.32	$18.30	$18.30
Purchase #5	$97.44	11.710%	$108.8502	$108.85	$108.85	$108.90
Purchase #6	$69.39	3.522%	$71.8339	$71.83	$71.85	$71.80
Purchase #7	$11.41	3.853%	$11.8496	$11.85	$11.85	$11.80
7 purchase totals =	$778.38		$837.7944	$837.78	$837.75	$837.70