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	$79.64	12.142%	$89.3099	$89.31	$89.30	$89.30
Purchase #2	$146.91	9.316%	$160.5961	$160.60	$160.60	$160.60
Purchase #3	$165.41	6.514%	$176.1848	$176.18	$176.20	$176.20
Purchase #4	$70.91	10.300%	$78.2137	$78.21	$78.20	$78.20
Purchase #5	$159.82	6.311%	$169.9062	$169.91	$169.90	$169.90
Purchase #6	$154.90	7.173%	$166.011	$166.01	$166.00	$166.00
Purchase #7	$94.31	13.237%	$106.7938	$106.79	$106.80	$106.80
7 purchase totals =	$871.90		$947.0155	$947.01	$947.00	$947.00