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	$83.74	6.687%	$89.3397	$89.34	$89.35	$89.30
Purchase #2	$73.46	10.805%	$81.3974	$81.40	$81.40	$81.40
Purchase #3	$65.77	7.617%	$70.7797	$70.78	$70.80	$70.80
Purchase #4	$25.27	9.176%	$27.5888	$27.59	$27.60	$27.60
Purchase #5	$58.44	5.700%	$61.7711	$61.77	$61.75	$61.80
Purchase #6	$232.65	10.427%	$256.9084	$256.91	$256.90	$256.90
Purchase #7	$13.94	9.775%	$15.3026	$15.30	$15.30	$15.30
7 purchase totals =	$553.27		$603.0877	$603.09	$603.10	$603.10