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	$81.78	9.320%	$89.4019	$89.40	$89.40	$89.40
Purchase #2	$239.80	6.508%	$255.4062	$255.41	$255.40	$255.40
Purchase #3	$65.46	12.594%	$73.704	$73.70	$73.70	$73.70
Purchase #4	$36.87	13.340%	$41.7885	$41.79	$41.80	$41.80
Purchase #5	$150.37	12.346%	$168.9347	$168.93	$168.95	$168.90
Purchase #6	$166.61	9.652%	$182.6912	$182.69	$182.70	$182.70
Purchase #7	$174.68	10.648%	$193.2799	$193.28	$193.30	$193.30
7 purchase totals =	$915.57		$1,005.2064	$1,005.20	$1,005.25	$1,005.20