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	$54.34	6.681%	$57.9705	$57.97	$57.95	$58.00
Purchase #2	$241.76	12.626%	$272.2846	$272.28	$272.30	$272.30
Purchase #3	$78.25	9.636%	$85.7902	$85.79	$85.80	$85.80
Purchase #4	$91.91	5.422%	$96.8934	$96.89	$96.90	$96.90
Purchase #5	$232.40	12.694%	$261.9009	$261.90	$261.90	$261.90
Purchase #6	$42.54	11.757%	$47.5414	$47.54	$47.55	$47.50
Purchase #7	$102.77	8.562%	$111.5692	$111.57	$111.55	$111.60
7 purchase totals =	$843.97		$933.9502	$933.94	$933.95	$934.00