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	$248.64	8.290%	$269.2523	$269.25	$269.25	$269.30
Purchase #2	$115.94	7.116%	$124.1903	$124.19	$124.20	$124.20
Purchase #3	$205.31	6.635%	$218.9323	$218.93	$218.95	$218.90
Purchase #4	$79.69	12.167%	$89.3859	$89.39	$89.40	$89.40
Purchase #5	$64.32	9.189%	$70.2304	$70.23	$70.25	$70.20
Purchase #6	$131.27	8.185%	$142.0144	$142.01	$142.00	$142.00
Purchase #7	$158.83	12.871%	$179.273	$179.27	$179.25	$179.30
7 purchase totals =	$1,004.00		$1,093.2786	$1,093.27	$1,093.30	$1,093.30