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	$247.65	9.242%	$270.5378	$270.54	$270.55	$270.50
Purchase #2	$179.40	9.765%	$196.9184	$196.92	$196.90	$196.90
Purchase #3	$14.28	5.610%	$15.0811	$15.08	$15.10	$15.10
Purchase #4	$39.62	7.809%	$42.7139	$42.71	$42.70	$42.70
Purchase #5	$55.77	11.719%	$62.3057	$62.31	$62.30	$62.30
Purchase #6	$218.25	11.744%	$243.8813	$243.88	$243.90	$243.90
Purchase #7	$156.50	5.833%	$165.6286	$165.63	$165.65	$165.60
7 purchase totals =	$911.47		$997.0668	$997.07	$997.10	$997.00