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	$26.44	13.146%	$29.9158	$29.92	$29.90	$29.90
Purchase #2	$72.66	4.643%	$76.0336	$76.03	$76.05	$76.00
Purchase #3	$68.43	12.280%	$76.8332	$76.83	$76.85	$76.80
Purchase #4	$206.70	6.665%	$220.4766	$220.48	$220.50	$220.50
Purchase #5	$242.89	10.814%	$269.1561	$269.16	$269.15	$269.20
Purchase #6	$72.59	13.118%	$82.1124	$82.11	$82.10	$82.10
Purchase #7	$245.90	5.694%	$259.9015	$259.90	$259.90	$259.90
7 purchase totals =	$935.61		$1,014.4292	$1,014.43	$1,014.45	$1,014.40