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	$5.38	10.841%	$5.9632	$5.96	$5.95	$6.00
Purchase #2	$69.43	12.813%	$78.3261	$78.33	$78.35	$78.30
Purchase #3	$37.45	9.211%	$40.8995	$40.90	$40.90	$40.90
Purchase #4	$177.97	12.758%	$200.6754	$200.68	$200.70	$200.70
Purchase #5	$72.27	8.417%	$78.353	$78.35	$78.35	$78.40
Purchase #6	$221.26	4.531%	$231.2853	$231.29	$231.30	$231.30
Purchase #7	$210.82	5.341%	$222.0799	$222.08	$222.10	$222.10
7 purchase totals =	$794.58		$857.5824	$857.59	$857.65	$857.70