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	$13.73	3.860%	$14.26	$14.26	$14.25	$14.30
Purchase #2	$198.89	13.771%	$226.2791	$226.28	$226.30	$226.30
Purchase #3	$112.83	10.729%	$124.9355	$124.94	$124.95	$124.90
Purchase #4	$226.38	5.272%	$238.3148	$238.31	$238.30	$238.30
Purchase #5	$137.27	5.672%	$145.056	$145.06	$145.05	$145.10
Purchase #6	$67.46	7.687%	$72.6457	$72.65	$72.65	$72.60
Purchase #7	$33.83	4.407%	$35.3209	$35.32	$35.30	$35.30
7 purchase totals =	$790.39		$856.8120	$856.82	$856.80	$856.80