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	$78.31	5.108%	$82.3101	$82.31	$82.30	$82.30
Purchase #2	$19.27	4.125%	$20.0649	$20.06	$20.05	$20.10
Purchase #3	$64.30	3.614%	$66.6238	$66.62	$66.60	$66.60
Purchase #4	$153.54	3.771%	$159.33	$159.33	$159.35	$159.30
Purchase #5	$236.60	3.729%	$245.4228	$245.42	$245.40	$245.40
Purchase #6	$109.80	12.680%	$123.7226	$123.72	$123.70	$123.70
Purchase #7	$24.51	5.231%	$25.7921	$25.79	$25.80	$25.80
7 purchase totals =	$686.33		$723.2663	$723.25	$723.20	$723.20