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	$52.44	4.526%	$54.8134	$54.81	$54.80	$54.80
Purchase #2	$215.69	6.387%	$229.4661	$229.47	$229.45	$229.50
Purchase #3	$239.72	5.782%	$253.5806	$253.58	$253.60	$253.60
Purchase #4	$119.82	8.404%	$129.8897	$129.89	$129.90	$129.90
Purchase #5	$101.95	3.619%	$105.6396	$105.64	$105.65	$105.60
Purchase #6	$209.59	12.298%	$235.3654	$235.37	$235.35	$235.40
Purchase #7	$242.91	11.372%	$270.5337	$270.53	$270.55	$270.50
7 purchase totals =	$1,182.12		$1,279.2885	$1,279.29	$1,279.30	$1,279.30