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	$239.32	11.328%	$266.4302	$266.43	$266.45	$266.40
Purchase #2	$96.98	13.249%	$109.8289	$109.83	$109.85	$109.80
Purchase #3	$80.77	5.797%	$85.4522	$85.45	$85.45	$85.50
Purchase #4	$36.83	6.252%	$39.1326	$39.13	$39.15	$39.10
Purchase #5	$25.43	10.699%	$28.1508	$28.15	$28.15	$28.20
Purchase #6	$231.56	13.672%	$263.2189	$263.22	$263.20	$263.20
Purchase #7	$31.66	11.190%	$35.2028	$35.20	$35.20	$35.20
7 purchase totals =	$742.55		$827.4164	$827.41	$827.45	$827.40