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	$175.86	3.429%	$181.8902	$181.89	$181.90	$181.90
Purchase #2	$124.48	13.219%	$140.935	$140.94	$140.95	$140.90
Purchase #3	$50.45	13.228%	$57.1235	$57.12	$57.10	$57.10
Purchase #4	$175.94	12.871%	$198.5852	$198.59	$198.60	$198.60
Purchase #5	$182.88	3.268%	$188.8565	$188.86	$188.85	$188.90
Purchase #6	$68.93	4.480%	$72.0181	$72.02	$72.00	$72.00
Purchase #7	$32.94	5.704%	$34.8189	$34.82	$34.80	$34.80
7 purchase totals =	$811.48		$874.2274	$874.24	$874.20	$874.20