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	$9.33	7.664%	$10.0451	$10.05	$10.05	$10.00
Purchase #2	$42.53	7.139%	$45.5662	$45.57	$45.55	$45.60
Purchase #3	$177.32	7.279%	$190.2271	$190.23	$190.25	$190.20
Purchase #4	$106.42	3.637%	$110.2905	$110.29	$110.30	$110.30
Purchase #5	$49.32	12.239%	$55.3563	$55.36	$55.35	$55.40
Purchase #6	$91.25	9.481%	$99.9014	$99.90	$99.90	$99.90
Purchase #7	$129.32	6.605%	$137.8616	$137.86	$137.85	$137.90
7 purchase totals =	$605.49		$649.2482	$649.26	$649.25	$649.30