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	$29.90	8.839%	$32.5429	$32.54	$32.55	$32.50
Purchase #2	$65.54	11.868%	$73.3183	$73.32	$73.30	$73.30
Purchase #3	$154.46	8.367%	$167.3837	$167.38	$167.40	$167.40
Purchase #4	$32.44	9.216%	$35.4297	$35.43	$35.45	$35.40
Purchase #5	$204.78	7.483%	$220.1037	$220.10	$220.10	$220.10
Purchase #6	$54.56	9.683%	$59.843	$59.84	$59.85	$59.80
Purchase #7	$67.88	10.852%	$75.2463	$75.25	$75.25	$75.20
7 purchase totals =	$609.56		$663.8676	$663.86	$663.90	$663.70