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	$10.52	3.607%	$10.8995	$10.90	$10.90	$10.90
Purchase #2	$189.52	5.103%	$199.1912	$199.19	$199.20	$199.20
Purchase #3	$237.45	13.630%	$269.8144	$269.81	$269.80	$269.80
Purchase #4	$36.63	3.270%	$37.8278	$37.83	$37.85	$37.80
Purchase #5	$131.76	8.463%	$142.9108	$142.91	$142.90	$142.90
Purchase #6	$176.55	7.571%	$189.9166	$189.92	$189.90	$189.90
Purchase #7	$222.72	11.507%	$248.3484	$248.35	$248.35	$248.30
7 purchase totals =	$1,005.15		$1,098.9087	$1,098.91	$1,098.90	$1,098.80