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	$56.55	5.104%	$59.4363	$59.44	$59.45	$59.40
Purchase #2	$19.87	6.178%	$21.0976	$21.10	$21.10	$21.10
Purchase #3	$70.92	9.861%	$77.9134	$77.91	$77.90	$77.90
Purchase #4	$187.43	9.816%	$205.8281	$205.83	$205.85	$205.80
Purchase #5	$160.29	13.558%	$182.0221	$182.02	$182.00	$182.00
Purchase #6	$111.87	7.558%	$120.3251	$120.33	$120.35	$120.30
Purchase #7	$37.36	13.598%	$42.4402	$42.44	$42.45	$42.40
7 purchase totals =	$644.29		$709.0628	$709.07	$709.10	$708.90