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	$78.61	11.812%	$87.8954	$87.90	$87.90	$87.90
Purchase #2	$39.85	12.688%	$44.9062	$44.91	$44.90	$44.90
Purchase #3	$99.64	11.740%	$111.3377	$111.34	$111.35	$111.30
Purchase #4	$26.51	8.871%	$28.8617	$28.86	$28.85	$28.90
Purchase #5	$116.70	8.686%	$126.8366	$126.84	$126.85	$126.80
Purchase #6	$156.73	7.393%	$168.317	$168.32	$168.30	$168.30
Purchase #7	$94.82	13.369%	$107.4965	$107.50	$107.50	$107.50
7 purchase totals =	$612.86		$675.6511	$675.67	$675.65	$675.60