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	$239.41	6.306%	$254.5072	$254.51	$254.50	$254.50
Purchase #2	$92.80	13.521%	$105.3475	$105.35	$105.35	$105.30
Purchase #3	$205.64	5.272%	$216.4813	$216.48	$216.50	$216.50
Purchase #4	$33.80	4.126%	$35.1946	$35.19	$35.20	$35.20
Purchase #5	$116.78	12.474%	$131.3471	$131.35	$131.35	$131.30
Purchase #6	$57.95	5.278%	$61.0086	$61.01	$61.00	$61.00
Purchase #7	$47.40	9.837%	$52.0627	$52.06	$52.05	$52.10
7 purchase totals =	$793.78		$855.9490	$855.95	$855.95	$855.90