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	$40.35	12.505%	$45.3958	$45.40	$45.40	$45.40
Purchase #2	$140.73	3.279%	$145.3445	$145.34	$145.35	$145.30
Purchase #3	$224.97	5.400%	$237.1184	$237.12	$237.10	$237.10
Purchase #4	$220.56	4.107%	$229.6184	$229.62	$229.60	$229.60
Purchase #5	$199.52	4.556%	$208.6101	$208.61	$208.60	$208.60
Purchase #6	$72.96	13.579%	$82.8672	$82.87	$82.85	$82.90
Purchase #7	$212.57	4.761%	$222.6905	$222.69	$222.70	$222.70
7 purchase totals =	$1,111.66		$1,171.6449	$1,171.65	$1,171.60	$1,171.60