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	$31.28	6.258%	$33.2375	$33.24	$33.25	$33.20
Purchase #2	$200.45	4.552%	$209.5745	$209.57	$209.55	$209.60
Purchase #3	$29.90	3.740%	$31.0183	$31.02	$31.00	$31.00
Purchase #4	$51.66	11.389%	$57.5436	$57.54	$57.55	$57.50
Purchase #5	$223.66	3.175%	$230.7612	$230.76	$230.75	$230.80
Purchase #6	$216.30	10.180%	$238.3193	$238.32	$238.30	$238.30
Purchase #7	$180.82	5.564%	$190.8808	$190.88	$190.90	$190.90
7 purchase totals =	$934.07		$991.3352	$991.33	$991.30	$991.30