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	$18.71	8.537%	$20.3073	$20.31	$20.30	$20.30
Purchase #2	$120.95	8.307%	$130.9973	$131.00	$131.00	$131.00
Purchase #3	$166.56	12.698%	$187.7098	$187.71	$187.70	$187.70
Purchase #4	$85.40	5.174%	$89.8186	$89.82	$89.80	$89.80
Purchase #5	$39.76	5.841%	$42.0824	$42.08	$42.10	$42.10
Purchase #6	$53.89	8.719%	$58.5887	$58.59	$58.60	$58.60
Purchase #7	$213.57	5.796%	$225.9485	$225.95	$225.95	$225.90
7 purchase totals =	$698.84		$755.4526	$755.46	$755.45	$755.40