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	$131.74	11.281%	$146.6016	$146.60	$146.60	$146.60
Purchase #2	$117.32	5.566%	$123.85	$123.85	$123.85	$123.90
Purchase #3	$168.88	11.475%	$188.259	$188.26	$188.25	$188.30
Purchase #4	$105.57	6.400%	$112.3265	$112.33	$112.35	$112.30
Purchase #5	$245.51	6.517%	$261.5099	$261.51	$261.50	$261.50
Purchase #6	$79.46	9.231%	$86.795	$86.80	$86.80	$86.80
Purchase #7	$149.88	7.192%	$160.6594	$160.66	$160.65	$160.70
7 purchase totals =	$998.36		$1,080.0014	$1,080.01	$1,080.00	$1,080.10