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	$42.40	11.744%	$47.3795	$47.38	$47.40	$47.40
Purchase #2	$92.90	4.834%	$97.3908	$97.39	$97.40	$97.40
Purchase #3	$203.92	9.450%	$223.1904	$223.19	$223.20	$223.20
Purchase #4	$58.78	4.859%	$61.6361	$61.64	$61.65	$61.60
Purchase #5	$79.52	10.214%	$87.6422	$87.64	$87.65	$87.60
Purchase #6	$187.66	4.752%	$196.5776	$196.58	$196.60	$196.60
Purchase #7	$142.61	11.413%	$158.8861	$158.89	$158.90	$158.90
7 purchase totals =	$807.79		$872.7027	$872.71	$872.80	$872.70