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	$51.74	4.778%	$54.2121	$54.21	$54.20	$54.20
Purchase #2	$95.69	11.746%	$106.9297	$106.93	$106.95	$106.90
Purchase #3	$145.71	4.352%	$152.0513	$152.05	$152.05	$152.10
Purchase #4	$161.86	6.541%	$172.4473	$172.45	$172.45	$172.40
Purchase #5	$185.82	12.221%	$208.5291	$208.53	$208.55	$208.50
Purchase #6	$246.82	13.834%	$280.9651	$280.97	$280.95	$281.00
Purchase #7	$166.61	4.738%	$174.504	$174.50	$174.50	$174.50
7 purchase totals =	$1,054.25		$1,149.6386	$1,149.64	$1,149.65	$1,149.60