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	$56.96	9.489%	$62.3649	$62.36	$62.35	$62.40
Purchase #2	$89.62	12.556%	$100.8727	$100.87	$100.85	$100.90
Purchase #3	$238.72	13.250%	$270.3504	$270.35	$270.35	$270.40
Purchase #4	$43.31	5.844%	$45.841	$45.84	$45.85	$45.80
Purchase #5	$26.39	11.371%	$29.3908	$29.39	$29.40	$29.40
Purchase #6	$131.59	6.571%	$140.2368	$140.24	$140.25	$140.20
Purchase #7	$29.70	12.715%	$33.4764	$33.48	$33.50	$33.50
7 purchase totals =	$616.29		$682.5330	$682.53	$682.55	$682.60