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	$141.56	12.373%	$159.0752	$159.08	$159.10	$159.10
Purchase #2	$196.99	7.312%	$211.3939	$211.39	$211.40	$211.40
Purchase #3	$171.41	13.176%	$193.995	$194.00	$194.00	$194.00
Purchase #4	$103.90	10.585%	$114.8978	$114.90	$114.90	$114.90
Purchase #5	$247.95	3.442%	$256.4844	$256.48	$256.50	$256.50
Purchase #6	$27.50	3.375%	$28.4281	$28.43	$28.45	$28.40
Purchase #7	$50.27	9.850%	$55.2216	$55.22	$55.20	$55.20
7 purchase totals =	$939.58		$1,019.4960	$1,019.50	$1,019.55	$1,019.50