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	$243.95	13.293%	$276.3783	$276.38	$276.40	$276.40
Purchase #2	$120.56	10.172%	$132.8234	$132.82	$132.80	$132.80
Purchase #3	$120.27	5.415%	$126.7826	$126.78	$126.80	$126.80
Purchase #4	$202.66	11.446%	$225.8565	$225.86	$225.85	$225.90
Purchase #5	$78.58	6.102%	$83.375	$83.38	$83.40	$83.40
Purchase #6	$49.71	12.275%	$55.8119	$55.81	$55.80	$55.80
Purchase #7	$88.90	11.398%	$99.0328	$99.03	$99.05	$99.00
7 purchase totals =	$904.63		$1,000.0605	$1,000.06	$1,000.10	$1,000.10