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	$92.90	4.652%	$97.2217	$97.22	$97.20	$97.20
Purchase #2	$90.81	10.334%	$100.1943	$100.19	$100.20	$100.20
Purchase #3	$125.34	11.434%	$139.6714	$139.67	$139.65	$139.70
Purchase #4	$102.62	7.115%	$109.9214	$109.92	$109.90	$109.90
Purchase #5	$182.84	4.690%	$191.4152	$191.42	$191.40	$191.40
Purchase #6	$189.82	3.713%	$196.868	$196.87	$196.85	$196.90
Purchase #7	$231.58	13.309%	$262.401	$262.40	$262.40	$262.40
7 purchase totals =	$1,015.91		$1,097.6930	$1,097.69	$1,097.60	$1,097.70