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	$25.81	6.320%	$27.4412	$27.44	$27.45	$27.40
Purchase #2	$54.49	8.686%	$59.223	$59.22	$59.20	$59.20
Purchase #3	$58.73	13.874%	$66.8782	$66.88	$66.90	$66.90
Purchase #4	$113.47	12.748%	$127.9352	$127.94	$127.95	$127.90
Purchase #5	$135.66	8.418%	$147.0799	$147.08	$147.10	$147.10
Purchase #6	$31.97	4.635%	$33.4518	$33.45	$33.45	$33.50
Purchase #7	$133.83	12.562%	$150.6417	$150.64	$150.65	$150.60
7 purchase totals =	$553.96		$612.6510	$612.65	$612.70	$612.60