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	$249.49	11.255%	$277.5701	$277.57	$277.55	$277.60
Purchase #2	$73.69	12.582%	$82.9617	$82.96	$82.95	$83.00
Purchase #3	$118.38	4.307%	$123.4786	$123.48	$123.50	$123.50
Purchase #4	$61.69	4.577%	$64.5136	$64.51	$64.50	$64.50
Purchase #5	$7.34	8.667%	$7.9762	$7.98	$8.00	$8.00
Purchase #6	$178.76	3.548%	$185.1024	$185.10	$185.10	$185.10
Purchase #7	$118.55	8.276%	$128.3612	$128.36	$128.35	$128.40
7 purchase totals =	$807.90		$869.9638	$869.96	$869.95	$870.10