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	$52.31	13.287%	$59.2604	$59.26	$59.25	$59.30
Purchase #2	$110.65	11.446%	$123.315	$123.32	$123.30	$123.30
Purchase #3	$57.45	9.861%	$63.1151	$63.12	$63.10	$63.10
Purchase #4	$6.92	5.589%	$7.3068	$7.31	$7.30	$7.30
Purchase #5	$108.65	9.328%	$118.7849	$118.78	$118.80	$118.80
Purchase #6	$93.95	11.682%	$104.9252	$104.93	$104.95	$104.90
Purchase #7	$218.87	6.559%	$233.2257	$233.23	$233.25	$233.20
7 purchase totals =	$648.80		$709.9331	$709.95	$709.95	$709.90