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	$9.89	11.731%	$11.0502	$11.05	$11.05	$11.10
Purchase #2	$77.60	6.444%	$82.6005	$82.60	$82.60	$82.60
Purchase #3	$82.77	5.750%	$87.5293	$87.53	$87.55	$87.50
Purchase #4	$76.48	3.242%	$78.9595	$78.96	$78.95	$79.00
Purchase #5	$180.56	8.504%	$195.9148	$195.91	$195.90	$195.90
Purchase #6	$38.99	9.477%	$42.6851	$42.69	$42.70	$42.70
Purchase #7	$28.56	12.649%	$32.1726	$32.17	$32.15	$32.20
7 purchase totals =	$494.85		$530.9120	$530.91	$530.90	$531.00