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	$76.88	3.678%	$79.7076	$79.71	$79.70	$79.70
Purchase #2	$128.59	13.519%	$145.9741	$145.97	$145.95	$146.00
Purchase #3	$130.76	9.254%	$142.8605	$142.86	$142.85	$142.90
Purchase #4	$18.84	9.313%	$20.5946	$20.59	$20.60	$20.60
Purchase #5	$241.28	10.446%	$266.4841	$266.48	$266.50	$266.50
Purchase #6	$90.34	5.816%	$95.5942	$95.59	$95.60	$95.60
Purchase #7	$246.50	5.365%	$259.7247	$259.72	$259.70	$259.70
7 purchase totals =	$933.19		$1,010.9398	$1,010.92	$1,010.90	$1,011.00