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	$120.66	13.128%	$136.5002	$136.50	$136.50	$136.50
Purchase #2	$75.49	13.598%	$85.7551	$85.76	$85.75	$85.80
Purchase #3	$104.78	6.478%	$111.5676	$111.57	$111.55	$111.60
Purchase #4	$36.90	7.616%	$39.7103	$39.71	$39.70	$39.70
Purchase #5	$7.35	12.218%	$8.248	$8.25	$8.25	$8.20
Purchase #6	$51.73	10.384%	$57.1016	$57.10	$57.10	$57.10
Purchase #7	$6.56	12.202%	$7.3605	$7.36	$7.35	$7.40
7 purchase totals =	$403.47		$446.2433	$446.25	$446.20	$446.30