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	$94.94	9.218%	$103.6916	$103.69	$103.70	$103.70
Purchase #2	$38.86	12.130%	$43.5737	$43.57	$43.55	$43.60
Purchase #3	$166.43	9.546%	$182.3174	$182.32	$182.30	$182.30
Purchase #4	$150.30	10.731%	$166.4287	$166.43	$166.45	$166.40
Purchase #5	$104.28	12.390%	$117.2003	$117.20	$117.20	$117.20
Purchase #6	$89.86	5.756%	$95.0323	$95.03	$95.05	$95.00
Purchase #7	$70.59	9.656%	$77.4062	$77.41	$77.40	$77.40
7 purchase totals =	$715.26		$785.6502	$785.65	$785.65	$785.60