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	$8.39	9.320%	$9.1719	$9.17	$9.15	$9.20
Purchase #2	$123.54	8.827%	$134.4449	$134.44	$134.45	$134.40
Purchase #3	$183.59	3.502%	$190.0193	$190.02	$190.00	$190.00
Purchase #4	$38.78	4.300%	$40.4475	$40.45	$40.45	$40.40
Purchase #5	$65.79	8.398%	$71.315	$71.32	$71.30	$71.30
Purchase #6	$133.71	10.606%	$147.8913	$147.89	$147.90	$147.90
Purchase #7	$187.59	13.731%	$213.348	$213.35	$213.35	$213.30
7 purchase totals =	$741.39		$806.6379	$806.64	$806.60	$806.50