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	$250.92	11.743%	$280.3855	$280.39	$280.40	$280.40
Purchase #2	$52.25	8.591%	$56.7388	$56.74	$56.75	$56.70
Purchase #3	$208.57	13.829%	$237.4131	$237.41	$237.40	$237.40
Purchase #4	$148.48	10.474%	$164.0318	$164.03	$164.05	$164.00
Purchase #5	$199.67	6.826%	$213.2995	$213.30	$213.30	$213.30
Purchase #6	$9.59	7.529%	$10.312	$10.31	$10.30	$10.30
Purchase #7	$50.91	13.336%	$57.6994	$57.70	$57.70	$57.70
7 purchase totals =	$920.39		$1,019.8801	$1,019.88	$1,019.90	$1,019.80