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	$245.41	13.625%	$278.8471	$278.85	$278.85	$278.80
Purchase #2	$27.39	10.795%	$30.3468	$30.35	$30.35	$30.30
Purchase #3	$59.30	10.545%	$65.5532	$65.55	$65.55	$65.60
Purchase #4	$31.42	12.120%	$35.2281	$35.23	$35.25	$35.20
Purchase #5	$156.81	9.372%	$171.5062	$171.51	$171.50	$171.50
Purchase #6	$150.32	4.124%	$156.5192	$156.52	$156.50	$156.50
Purchase #7	$85.77	5.353%	$90.3613	$90.36	$90.35	$90.40
7 purchase totals =	$756.42		$828.3619	$828.37	$828.35	$828.30