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	$154.64	8.646%	$168.0102	$168.01	$168.00	$168.00
Purchase #2	$27.92	4.614%	$29.2082	$29.21	$29.20	$29.20
Purchase #3	$192.49	12.168%	$215.9122	$215.91	$215.90	$215.90
Purchase #4	$51.32	4.229%	$53.4903	$53.49	$53.50	$53.50
Purchase #5	$115.94	13.405%	$131.4818	$131.48	$131.50	$131.50
Purchase #6	$48.64	12.586%	$54.7618	$54.76	$54.75	$54.80
Purchase #7	$245.34	11.201%	$272.8205	$272.82	$272.80	$272.80
7 purchase totals =	$836.29		$925.6850	$925.68	$925.65	$925.70