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	$189.64	8.570%	$205.8921	$205.89	$205.90	$205.90
Purchase #2	$115.48	11.736%	$129.0327	$129.03	$129.05	$129.00
Purchase #3	$44.46	12.117%	$49.8472	$49.85	$49.85	$49.80
Purchase #4	$116.52	9.760%	$127.8924	$127.89	$127.90	$127.90
Purchase #5	$129.59	4.602%	$135.5537	$135.55	$135.55	$135.60
Purchase #6	$40.25	5.109%	$42.3064	$42.31	$42.30	$42.30
Purchase #7	$49.42	13.232%	$55.9593	$55.96	$55.95	$56.00
7 purchase totals =	$685.36		$746.4838	$746.48	$746.50	$746.50