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	$76.78	3.269%	$79.2899	$79.29	$79.30	$79.30
Purchase #2	$64.31	12.664%	$72.4542	$72.45	$72.45	$72.50
Purchase #3	$221.96	10.127%	$244.4379	$244.44	$244.45	$244.40
Purchase #4	$42.78	10.870%	$47.4302	$47.43	$47.45	$47.40
Purchase #5	$128.44	6.224%	$136.4341	$136.43	$136.45	$136.40
Purchase #6	$35.45	8.266%	$38.3803	$38.38	$38.40	$38.40
Purchase #7	$122.28	4.812%	$128.1641	$128.16	$128.15	$128.20
7 purchase totals =	$692.00		$746.5907	$746.58	$746.65	$746.60