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	$81.30	10.587%	$89.9072	$89.91	$89.90	$89.90
Purchase #2	$167.33	3.691%	$173.5062	$173.51	$173.50	$173.50
Purchase #3	$173.41	8.545%	$188.2279	$188.23	$188.25	$188.20
Purchase #4	$79.85	8.161%	$86.3666	$86.37	$86.35	$86.40
Purchase #5	$203.26	10.192%	$223.9763	$223.98	$224.00	$224.00
Purchase #6	$49.26	8.381%	$53.3885	$53.39	$53.40	$53.40
Purchase #7	$247.81	6.702%	$264.4182	$264.42	$264.40	$264.40
7 purchase totals =	$1,002.22		$1,079.7909	$1,079.81	$1,079.80	$1,079.80