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	$235.57	3.445%	$243.6854	$243.69	$243.70	$243.70
Purchase #2	$211.49	5.669%	$223.4794	$223.48	$223.50	$223.50
Purchase #3	$237.91	5.468%	$250.9189	$250.92	$250.90	$250.90
Purchase #4	$13.55	12.420%	$15.2329	$15.23	$15.25	$15.20
Purchase #5	$238.46	13.187%	$269.9057	$269.91	$269.90	$269.90
Purchase #6	$121.64	13.411%	$137.9531	$137.95	$137.95	$138.00
Purchase #7	$33.59	13.545%	$38.1398	$38.14	$38.15	$38.10
7 purchase totals =	$1,092.21		$1,179.3152	$1,179.32	$1,179.35	$1,179.30