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	$250.93	11.339%	$279.383	$279.38	$279.40	$279.40
Purchase #2	$47.91	7.163%	$51.3418	$51.34	$51.35	$51.30
Purchase #3	$214.88	13.430%	$243.7384	$243.74	$243.75	$243.70
Purchase #4	$60.72	12.224%	$68.1424	$68.14	$68.15	$68.10
Purchase #5	$70.50	6.136%	$74.8259	$74.83	$74.85	$74.80
Purchase #6	$85.89	4.809%	$90.0205	$90.02	$90.00	$90.00
Purchase #7	$218.78	13.349%	$247.9849	$247.98	$248.00	$248.00
7 purchase totals =	$949.61		$1,055.4369	$1,055.43	$1,055.50	$1,055.30