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	$16.43	8.181%	$17.7741	$17.77	$17.75	$17.80
Purchase #2	$37.66	3.166%	$38.8523	$38.85	$38.85	$38.90
Purchase #3	$229.70	5.726%	$242.8526	$242.85	$242.85	$242.90
Purchase #4	$77.66	5.273%	$81.755	$81.76	$81.75	$81.80
Purchase #5	$73.95	6.347%	$78.6436	$78.64	$78.65	$78.60
Purchase #6	$244.86	5.783%	$259.0203	$259.02	$259.00	$259.00
Purchase #7	$75.40	3.842%	$78.2969	$78.30	$78.30	$78.30
7 purchase totals =	$755.66		$797.1948	$797.19	$797.15	$797.30