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	$99.48	11.568%	$110.9878	$110.99	$111.00	$111.00
Purchase #2	$117.59	11.586%	$131.214	$131.21	$131.20	$131.20
Purchase #3	$116.68	3.321%	$120.5549	$120.55	$120.55	$120.60
Purchase #4	$171.53	8.703%	$186.4583	$186.46	$186.45	$186.50
Purchase #5	$123.84	13.184%	$140.1671	$140.17	$140.15	$140.20
Purchase #6	$75.43	13.641%	$85.7194	$85.72	$85.70	$85.70
Purchase #7	$101.34	3.702%	$105.0916	$105.09	$105.10	$105.10
7 purchase totals =	$805.89		$880.1931	$880.19	$880.15	$880.30