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	$126.65	10.837%	$140.3751	$140.38	$140.40	$140.40
Purchase #2	$116.42	10.677%	$128.8502	$128.85	$128.85	$128.90
Purchase #3	$124.68	12.544%	$140.3199	$140.32	$140.30	$140.30
Purchase #4	$80.77	10.691%	$89.4051	$89.41	$89.40	$89.40
Purchase #5	$189.52	5.438%	$199.8261	$199.83	$199.85	$199.80
Purchase #6	$171.29	6.675%	$182.7236	$182.72	$182.70	$182.70
Purchase #7	$27.90	10.114%	$30.7218	$30.72	$30.70	$30.70
7 purchase totals =	$837.23		$912.2218	$912.23	$912.20	$912.20