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	$124.82	11.387%	$139.0333	$139.03	$139.05	$139.00
Purchase #2	$203.58	12.609%	$229.2494	$229.25	$229.25	$229.20
Purchase #3	$234.61	5.514%	$247.5464	$247.55	$247.55	$247.50
Purchase #4	$72.63	6.490%	$77.3437	$77.34	$77.35	$77.30
Purchase #5	$84.40	6.305%	$89.7214	$89.72	$89.70	$89.70
Purchase #6	$223.80	11.197%	$248.8589	$248.86	$248.85	$248.90
Purchase #7	$181.31	5.662%	$191.5758	$191.58	$191.60	$191.60
7 purchase totals =	$1,125.15		$1,223.3289	$1,223.33	$1,223.35	$1,223.20