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	$36.81	7.445%	$39.5505	$39.55	$39.55	$39.60
Purchase #2	$213.81	13.622%	$242.9352	$242.94	$242.95	$242.90
Purchase #3	$83.94	4.502%	$87.719	$87.72	$87.70	$87.70
Purchase #4	$222.35	4.855%	$233.1451	$233.15	$233.15	$233.10
Purchase #5	$124.32	9.554%	$136.1975	$136.20	$136.20	$136.20
Purchase #6	$160.66	4.458%	$167.8222	$167.82	$167.80	$167.80
Purchase #7	$167.25	10.682%	$185.1156	$185.12	$185.10	$185.10
7 purchase totals =	$1,009.14		$1,092.4851	$1,092.50	$1,092.45	$1,092.40