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	$11.51	3.690%	$11.9347	$11.93	$11.95	$11.90
Purchase #2	$93.68	12.711%	$105.5877	$105.59	$105.60	$105.60
Purchase #3	$181.95	4.150%	$189.5009	$189.50	$189.50	$189.50
Purchase #4	$131.59	5.710%	$139.1038	$139.10	$139.10	$139.10
Purchase #5	$52.72	13.673%	$59.9284	$59.93	$59.95	$59.90
Purchase #6	$99.26	4.431%	$103.6582	$103.66	$103.65	$103.70
Purchase #7	$198.86	6.352%	$211.4916	$211.49	$211.50	$211.50
7 purchase totals =	$769.57		$821.2053	$821.20	$821.25	$821.20