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	$125.52	10.722%	$138.9783	$138.98	$139.00	$139.00
Purchase #2	$69.52	4.676%	$72.7708	$72.77	$72.75	$72.80
Purchase #3	$243.50	11.231%	$270.8475	$270.85	$270.85	$270.80
Purchase #4	$104.86	4.409%	$109.4833	$109.48	$109.50	$109.50
Purchase #5	$229.89	12.225%	$257.9941	$257.99	$258.00	$258.00
Purchase #6	$144.59	4.433%	$150.9997	$151.00	$151.00	$151.00
Purchase #7	$82.27	13.478%	$93.3584	$93.36	$93.35	$93.40
7 purchase totals =	$1,000.15		$1,094.4321	$1,094.43	$1,094.45	$1,094.50