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	$220.35	11.412%	$245.4963	$245.50	$245.50	$245.50
Purchase #2	$142.73	6.243%	$151.6406	$151.64	$151.65	$151.60
Purchase #3	$31.41	9.193%	$34.2975	$34.30	$34.30	$34.30
Purchase #4	$32.58	12.736%	$36.7294	$36.73	$36.75	$36.70
Purchase #5	$250.85	5.483%	$264.6041	$264.60	$264.60	$264.60
Purchase #6	$99.31	3.239%	$102.5267	$102.53	$102.55	$102.50
Purchase #7	$234.30	4.751%	$245.4316	$245.43	$245.45	$245.40
7 purchase totals =	$1,011.53		$1,080.7262	$1,080.73	$1,080.80	$1,080.60