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	$69.82	12.814%	$78.7667	$78.77	$78.75	$78.80
Purchase #2	$19.35	13.483%	$21.959	$21.96	$21.95	$22.00
Purchase #3	$162.86	7.385%	$174.8872	$174.89	$174.90	$174.90
Purchase #4	$76.98	11.179%	$85.5856	$85.59	$85.60	$85.60
Purchase #5	$86.63	8.656%	$94.1287	$94.13	$94.15	$94.10
Purchase #6	$111.84	4.447%	$116.8135	$116.81	$116.80	$116.80
Purchase #7	$20.52	4.517%	$21.4469	$21.45	$21.45	$21.40
7 purchase totals =	$548.00		$593.5876	$593.60	$593.60	$593.60