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	$85.34	4.672%	$89.3271	$89.33	$89.35	$89.30
Purchase #2	$106.93	4.301%	$111.5291	$111.53	$111.55	$111.50
Purchase #3	$243.67	9.685%	$267.2694	$267.27	$267.25	$267.30
Purchase #4	$152.55	10.750%	$168.9491	$168.95	$168.95	$168.90
Purchase #5	$116.44	8.801%	$126.6879	$126.69	$126.70	$126.70
Purchase #6	$5.99	6.836%	$6.3995	$6.40	$6.40	$6.40
Purchase #7	$42.53	13.395%	$48.2269	$48.23	$48.25	$48.20
7 purchase totals =	$753.45		$818.3890	$818.40	$818.45	$818.30