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	$39.26	3.295%	$40.5536	$40.55	$40.55	$40.60
Purchase #2	$213.32	9.687%	$233.9843	$233.98	$234.00	$234.00
Purchase #3	$151.89	3.294%	$156.8933	$156.89	$156.90	$156.90
Purchase #4	$249.68	12.839%	$281.7364	$281.74	$281.75	$281.70
Purchase #5	$214.82	12.807%	$242.332	$242.33	$242.35	$242.30
Purchase #6	$163.42	11.782%	$182.6741	$182.67	$182.65	$182.70
Purchase #7	$17.47	7.228%	$18.7327	$18.73	$18.75	$18.70
7 purchase totals =	$1,049.86		$1,156.9064	$1,156.89	$1,156.95	$1,156.90