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	$108.58	10.729%	$120.2295	$120.23	$120.25	$120.20
Purchase #2	$136.47	11.173%	$151.7178	$151.72	$151.70	$151.70
Purchase #3	$70.69	3.254%	$72.9903	$72.99	$73.00	$73.00
Purchase #4	$95.89	12.625%	$107.9961	$108.00	$108.00	$108.00
Purchase #5	$228.90	6.407%	$243.5656	$243.57	$243.55	$243.60
Purchase #6	$208.31	3.524%	$215.6508	$215.65	$215.65	$215.70
Purchase #7	$83.87	7.826%	$90.4337	$90.43	$90.45	$90.40
7 purchase totals =	$932.71		$1,002.5838	$1,002.59	$1,002.60	$1,002.60