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	$89.38	12.275%	$100.3514	$100.35	$100.35	$100.40
Purchase #2	$79.52	12.298%	$89.2994	$89.30	$89.30	$89.30
Purchase #3	$140.89	12.655%	$158.7196	$158.72	$158.70	$158.70
Purchase #4	$216.59	9.278%	$236.6852	$236.69	$236.70	$236.70
Purchase #5	$81.90	6.592%	$87.2988	$87.30	$87.30	$87.30
Purchase #6	$161.50	12.722%	$182.046	$182.05	$182.05	$182.00
Purchase #7	$97.42	5.793%	$103.0635	$103.06	$103.05	$103.10
7 purchase totals =	$867.20		$957.4639	$957.47	$957.45	$957.50