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	$112.83	6.664%	$120.349	$120.35	$120.35	$120.30
Purchase #2	$249.90	10.408%	$275.9096	$275.91	$275.90	$275.90
Purchase #3	$81.54	9.874%	$89.5913	$89.59	$89.60	$89.60
Purchase #4	$234.61	10.234%	$258.62	$258.62	$258.60	$258.60
Purchase #5	$69.80	8.409%	$75.6695	$75.67	$75.65	$75.70
Purchase #6	$54.25	6.593%	$57.8267	$57.83	$57.85	$57.80
Purchase #7	$205.93	9.713%	$225.932	$225.93	$225.95	$225.90
7 purchase totals =	$1,008.86		$1,103.8981	$1,103.90	$1,103.90	$1,103.80