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	$36.78	10.130%	$40.5058	$40.51	$40.50	$40.50
Purchase #2	$13.46	3.682%	$13.9556	$13.96	$13.95	$14.00
Purchase #3	$47.71	8.586%	$51.8064	$51.81	$51.80	$51.80
Purchase #4	$49.64	9.809%	$54.5092	$54.51	$54.50	$54.50
Purchase #5	$64.82	10.138%	$71.3915	$71.39	$71.40	$71.40
Purchase #6	$52.81	13.169%	$59.7645	$59.76	$59.75	$59.80
Purchase #7	$7.66	4.204%	$7.982	$7.98	$8.00	$8.00
7 purchase totals =	$272.88		$299.9150	$299.92	$299.90	$300.00