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	$30.27	13.711%	$34.4203	$34.42	$34.40	$34.40
Purchase #2	$147.91	12.856%	$166.9253	$166.93	$166.95	$166.90
Purchase #3	$51.56	3.346%	$53.2852	$53.29	$53.30	$53.30
Purchase #4	$210.95	7.639%	$227.0645	$227.06	$227.05	$227.10
Purchase #5	$127.49	3.587%	$132.0631	$132.06	$132.05	$132.10
Purchase #6	$245.31	12.175%	$275.1765	$275.18	$275.20	$275.20
Purchase #7	$202.97	3.423%	$209.9177	$209.92	$209.90	$209.90
7 purchase totals =	$1,016.46		$1,098.8526	$1,098.86	$1,098.85	$1,098.90