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	$229.87	11.214%	$255.6476	$255.65	$255.65	$255.60
Purchase #2	$137.68	3.631%	$142.6792	$142.68	$142.70	$142.70
Purchase #3	$70.73	11.348%	$78.7564	$78.76	$78.75	$78.80
Purchase #4	$45.46	4.591%	$47.5471	$47.55	$47.55	$47.50
Purchase #5	$113.88	6.186%	$120.9246	$120.92	$120.90	$120.90
Purchase #6	$189.79	5.122%	$199.511	$199.51	$199.50	$199.50
Purchase #7	$75.76	3.452%	$78.3752	$78.38	$78.40	$78.40
7 purchase totals =	$863.17		$923.4411	$923.45	$923.45	$923.40