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	$44.75	10.581%	$49.485	$49.49	$49.50	$49.50
Purchase #2	$145.53	11.340%	$162.0331	$162.03	$162.05	$162.00
Purchase #3	$158.37	6.223%	$168.2254	$168.23	$168.25	$168.20
Purchase #4	$49.69	10.824%	$55.0684	$55.07	$55.05	$55.10
Purchase #5	$30.98	13.240%	$35.0818	$35.08	$35.10	$35.10
Purchase #6	$72.75	13.653%	$82.6826	$82.68	$82.70	$82.70
Purchase #7	$21.46	13.330%	$24.3206	$24.32	$24.30	$24.30
7 purchase totals =	$523.53		$576.8969	$576.90	$576.95	$576.90