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	$87.96	12.640%	$99.0781	$99.08	$99.10	$99.10
Purchase #2	$93.88	12.745%	$105.845	$105.85	$105.85	$105.80
Purchase #3	$113.49	3.365%	$117.3089	$117.31	$117.30	$117.30
Purchase #4	$232.43	10.515%	$256.87	$256.87	$256.85	$256.90
Purchase #5	$100.30	3.199%	$103.5086	$103.51	$103.50	$103.50
Purchase #6	$194.83	4.566%	$203.7259	$203.73	$203.75	$203.70
Purchase #7	$132.87	7.129%	$142.3423	$142.34	$142.35	$142.30
7 purchase totals =	$955.76		$1,028.6788	$1,028.69	$1,028.70	$1,028.60