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	$126.68	12.836%	$142.9406	$142.94	$142.95	$142.90
Purchase #2	$42.56	12.374%	$47.8264	$47.83	$47.85	$47.80
Purchase #3	$29.72	3.874%	$30.8714	$30.87	$30.85	$30.90
Purchase #4	$86.78	4.307%	$90.5176	$90.52	$90.50	$90.50
Purchase #5	$152.29	6.691%	$162.4797	$162.48	$162.50	$162.50
Purchase #6	$88.93	3.288%	$91.854	$91.85	$91.85	$91.90
Purchase #7	$231.71	12.684%	$261.1001	$261.10	$261.10	$261.10
7 purchase totals =	$758.67		$827.5898	$827.59	$827.60	$827.60