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	$230.97	4.276%	$240.8463	$240.85	$240.85	$240.80
Purchase #2	$111.91	6.470%	$119.1506	$119.15	$119.15	$119.20
Purchase #3	$25.78	8.849%	$28.0613	$28.06	$28.05	$28.10
Purchase #4	$104.46	10.305%	$115.2246	$115.22	$115.20	$115.20
Purchase #5	$148.51	11.811%	$166.0505	$166.05	$166.05	$166.10
Purchase #6	$56.36	6.189%	$59.8481	$59.85	$59.85	$59.80
Purchase #7	$186.90	6.533%	$199.1102	$199.11	$199.10	$199.10
7 purchase totals =	$864.89		$928.2916	$928.29	$928.25	$928.30