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	$6.83	13.402%	$7.7454	$7.75	$7.75	$7.70
Purchase #2	$112.94	9.595%	$123.7766	$123.78	$123.80	$123.80
Purchase #3	$64.89	11.384%	$72.2771	$72.28	$72.30	$72.30
Purchase #4	$178.79	8.505%	$193.9961	$194.00	$194.00	$194.00
Purchase #5	$38.31	4.419%	$40.0029	$40.00	$40.00	$40.00
Purchase #6	$144.95	4.325%	$151.2191	$151.22	$151.20	$151.20
Purchase #7	$120.34	11.777%	$134.5124	$134.51	$134.50	$134.50
7 purchase totals =	$667.05		$723.5296	$723.54	$723.55	$723.50