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	$53.61	4.676%	$56.1168	$56.12	$56.10	$56.10
Purchase #2	$121.28	7.301%	$130.1347	$130.13	$130.15	$130.10
Purchase #3	$63.43	4.115%	$66.0401	$66.04	$66.05	$66.00
Purchase #4	$82.39	4.738%	$86.2936	$86.29	$86.30	$86.30
Purchase #5	$223.34	7.860%	$240.8945	$240.89	$240.90	$240.90
Purchase #6	$10.26	6.463%	$10.9231	$10.92	$10.90	$10.90
Purchase #7	$27.50	5.225%	$28.9369	$28.94	$28.95	$28.90
7 purchase totals =	$581.81		$619.3397	$619.33	$619.35	$619.20