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	$52.80	11.393%	$58.8155	$58.82	$58.80	$58.80
Purchase #2	$85.26	13.647%	$96.8954	$96.90	$96.90	$96.90
Purchase #3	$247.47	7.240%	$265.3868	$265.39	$265.40	$265.40
Purchase #4	$173.34	7.533%	$186.3977	$186.40	$186.40	$186.40
Purchase #5	$126.49	8.140%	$136.7863	$136.79	$136.80	$136.80
Purchase #6	$48.30	13.575%	$54.8567	$54.86	$54.85	$54.90
Purchase #7	$99.39	12.406%	$111.7203	$111.72	$111.70	$111.70
7 purchase totals =	$833.05		$910.8587	$910.88	$910.85	$910.90