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	$8.48	6.130%	$8.9998	$9.00	$9.00	$9.00
Purchase #2	$178.56	11.253%	$198.6534	$198.65	$198.65	$198.70
Purchase #3	$244.64	4.712%	$256.1674	$256.17	$256.15	$256.20
Purchase #4	$159.51	5.531%	$168.3325	$168.33	$168.35	$168.30
Purchase #5	$79.88	3.831%	$82.9402	$82.94	$82.95	$82.90
Purchase #6	$126.89	6.321%	$134.9107	$134.91	$134.90	$134.90
Purchase #7	$190.65	5.123%	$200.417	$200.42	$200.40	$200.40
7 purchase totals =	$988.61		$1,050.4210	$1,050.42	$1,050.40	$1,050.40