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	$99.92	12.450%	$112.36	$112.36	$112.35	$112.40
Purchase #2	$138.32	6.626%	$147.4851	$147.49	$147.50	$147.50
Purchase #3	$6.87	13.785%	$7.817	$7.82	$7.80	$7.80
Purchase #4	$35.96	4.119%	$37.4412	$37.44	$37.45	$37.40
Purchase #5	$176.53	13.551%	$200.4516	$200.45	$200.45	$200.50
Purchase #6	$31.43	6.861%	$33.5864	$33.59	$33.60	$33.60
Purchase #7	$80.87	11.141%	$89.8797	$89.88	$89.90	$89.90
7 purchase totals =	$569.90		$629.0210	$629.03	$629.05	$629.10