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	$17.82	11.468%	$19.8636	$19.86	$19.85	$19.90
Purchase #2	$180.49	7.675%	$194.3426	$194.34	$194.35	$194.30
Purchase #3	$164.35	7.206%	$176.1931	$176.19	$176.20	$176.20
Purchase #4	$94.97	6.184%	$100.8429	$100.84	$100.85	$100.80
Purchase #5	$180.78	8.801%	$196.6904	$196.69	$196.70	$196.70
Purchase #6	$73.58	13.277%	$83.3492	$83.35	$83.35	$83.30
Purchase #7	$76.32	13.703%	$86.7781	$86.78	$86.80	$86.80
7 purchase totals =	$788.31		$858.0599	$858.05	$858.10	$858.00