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	$157.54	5.455%	$166.1338	$166.13	$166.15	$166.10
Purchase #2	$72.79	8.288%	$78.8228	$78.82	$78.80	$78.80
Purchase #3	$231.62	12.459%	$260.4775	$260.48	$260.50	$260.50
Purchase #4	$88.59	13.131%	$100.2228	$100.22	$100.20	$100.20
Purchase #5	$166.70	4.608%	$174.3815	$174.38	$174.40	$174.40
Purchase #6	$136.91	11.425%	$152.552	$152.55	$152.55	$152.60
Purchase #7	$103.75	12.424%	$116.6399	$116.64	$116.65	$116.60
7 purchase totals =	$957.90		$1,049.2303	$1,049.22	$1,049.25	$1,049.20