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	$137.69	3.183%	$142.0727	$142.07	$142.05	$142.10
Purchase #2	$67.77	3.456%	$70.1121	$70.11	$70.10	$70.10
Purchase #3	$131.63	4.369%	$137.3809	$137.38	$137.40	$137.40
Purchase #4	$46.57	7.836%	$50.2192	$50.22	$50.20	$50.20
Purchase #5	$33.69	3.566%	$34.8914	$34.89	$34.90	$34.90
Purchase #6	$182.83	5.784%	$193.4049	$193.40	$193.40	$193.40
Purchase #7	$35.25	12.207%	$39.553	$39.55	$39.55	$39.60
7 purchase totals =	$635.43		$667.6342	$667.62	$667.60	$667.70