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	$84.64	5.401%	$89.2114	$89.21	$89.20	$89.20
Purchase #2	$101.27	9.480%	$110.8704	$110.87	$110.85	$110.90
Purchase #3	$246.31	5.281%	$259.3176	$259.32	$259.30	$259.30
Purchase #4	$157.51	13.723%	$179.1251	$179.13	$179.15	$179.10
Purchase #5	$139.87	7.649%	$150.5687	$150.57	$150.55	$150.60
Purchase #6	$28.63	8.624%	$31.0991	$31.10	$31.10	$31.10
Purchase #7	$239.33	11.324%	$266.4317	$266.43	$266.45	$266.40
7 purchase totals =	$997.56		$1,086.6240	$1,086.63	$1,086.60	$1,086.60