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	$36.38	12.544%	$40.9435	$40.94	$40.95	$40.90
Purchase #2	$99.59	10.391%	$109.9384	$109.94	$109.95	$109.90
Purchase #3	$124.31	10.479%	$137.3364	$137.34	$137.35	$137.30
Purchase #4	$123.37	8.510%	$133.8688	$133.87	$133.85	$133.90
Purchase #5	$10.39	3.415%	$10.7448	$10.74	$10.75	$10.70
Purchase #6	$20.25	11.320%	$22.5423	$22.54	$22.55	$22.50
Purchase #7	$84.81	3.592%	$87.8564	$87.86	$87.85	$87.90
7 purchase totals =	$499.10		$543.2306	$543.23	$543.25	$543.10