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	$78.87	13.343%	$89.3936	$89.39	$89.40	$89.40
Purchase #2	$215.97	12.708%	$243.4155	$243.42	$243.40	$243.40
Purchase #3	$120.63	8.200%	$130.5217	$130.52	$130.50	$130.50
Purchase #4	$205.57	10.640%	$227.4426	$227.44	$227.45	$227.40
Purchase #5	$241.74	9.544%	$264.8117	$264.81	$264.80	$264.80
Purchase #6	$104.25	8.147%	$112.7432	$112.74	$112.75	$112.70
Purchase #7	$39.28	5.426%	$41.4113	$41.41	$41.40	$41.40
7 purchase totals =	$1,006.31		$1,109.7396	$1,109.73	$1,109.70	$1,109.60