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	$27.80	7.518%	$29.89	$29.89	$29.90	$29.90
Purchase #2	$105.78	6.468%	$112.6219	$112.62	$112.60	$112.60
Purchase #3	$30.44	6.407%	$32.3903	$32.39	$32.40	$32.40
Purchase #4	$9.88	9.417%	$10.8104	$10.81	$10.80	$10.80
Purchase #5	$141.55	6.634%	$150.9404	$150.94	$150.95	$150.90
Purchase #6	$8.81	12.254%	$9.8896	$9.89	$9.90	$9.90
Purchase #7	$68.25	11.873%	$76.3533	$76.35	$76.35	$76.40
7 purchase totals =	$392.51		$422.8959	$422.89	$422.90	$422.90