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	$6.85	9.250%	$7.4836	$7.48	$7.50	$7.50
Purchase #2	$181.85	10.436%	$200.8279	$200.83	$200.85	$200.80
Purchase #3	$94.30	4.404%	$98.453	$98.45	$98.45	$98.50
Purchase #4	$49.71	9.554%	$54.4593	$54.46	$54.45	$54.50
Purchase #5	$189.71	3.565%	$196.4732	$196.47	$196.45	$196.50
Purchase #6	$207.28	3.528%	$214.5928	$214.59	$214.60	$214.60
Purchase #7	$19.40	3.143%	$20.0097	$20.01	$20.00	$20.00
7 purchase totals =	$749.10		$792.2995	$792.29	$792.30	$792.40