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	$124.76	9.661%	$136.8131	$136.81	$136.80	$136.80
Purchase #2	$187.92	4.528%	$196.429	$196.43	$196.45	$196.40
Purchase #3	$146.27	4.841%	$153.3509	$153.35	$153.35	$153.40
Purchase #4	$20.84	11.775%	$23.2939	$23.29	$23.30	$23.30
Purchase #5	$98.36	11.456%	$109.6281	$109.63	$109.65	$109.60
Purchase #6	$247.43	13.542%	$280.937	$280.94	$280.95	$280.90
Purchase #7	$177.25	6.726%	$189.1718	$189.17	$189.15	$189.20
7 purchase totals =	$1,002.83		$1,089.6238	$1,089.62	$1,089.65	$1,089.60