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	$115.35	4.509%	$120.5511	$120.55	$120.55	$120.60
Purchase #2	$178.39	10.165%	$196.5233	$196.52	$196.50	$196.50
Purchase #3	$96.36	7.869%	$103.9426	$103.94	$103.95	$103.90
Purchase #4	$223.94	10.279%	$246.9588	$246.96	$246.95	$247.00
Purchase #5	$34.94	6.820%	$37.3229	$37.32	$37.30	$37.30
Purchase #6	$119.63	10.316%	$131.971	$131.97	$131.95	$132.00
Purchase #7	$48.95	6.640%	$52.2003	$52.20	$52.20	$52.20
7 purchase totals =	$817.56		$889.4700	$889.46	$889.40	$889.50