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	$211.76	6.804%	$226.1682	$226.17	$226.15	$226.20
Purchase #2	$69.25	3.816%	$71.8926	$71.89	$71.90	$71.90
Purchase #3	$147.37	5.307%	$155.1909	$155.19	$155.20	$155.20
Purchase #4	$206.39	10.768%	$228.6141	$228.61	$228.60	$228.60
Purchase #5	$70.69	11.516%	$78.8307	$78.83	$78.85	$78.80
Purchase #6	$248.69	10.523%	$274.8596	$274.86	$274.85	$274.90
Purchase #7	$227.98	11.262%	$253.6551	$253.66	$253.65	$253.70
7 purchase totals =	$1,182.13		$1,289.2112	$1,289.21	$1,289.20	$1,289.30