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	$99.28	13.206%	$112.3909	$112.39	$112.40	$112.40
Purchase #2	$81.75	10.118%	$90.0215	$90.02	$90.00	$90.00
Purchase #3	$74.29	8.440%	$80.5601	$80.56	$80.55	$80.60
Purchase #4	$205.56	11.776%	$229.7667	$229.77	$229.75	$229.80
Purchase #5	$156.58	11.766%	$175.0032	$175.00	$175.00	$175.00
Purchase #6	$152.72	8.302%	$165.3988	$165.40	$165.40	$165.40
Purchase #7	$95.26	12.631%	$107.2923	$107.29	$107.30	$107.30
7 purchase totals =	$865.44		$960.4335	$960.43	$960.40	$960.50