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	$96.61	13.430%	$109.5847	$109.58	$109.60	$109.60
Purchase #2	$19.28	10.413%	$21.2876	$21.29	$21.30	$21.30
Purchase #3	$247.32	13.419%	$280.5079	$280.51	$280.50	$280.50
Purchase #4	$85.78	12.265%	$96.3009	$96.30	$96.30	$96.30
Purchase #5	$77.96	4.277%	$81.2943	$81.29	$81.30	$81.30
Purchase #6	$112.43	6.611%	$119.8627	$119.86	$119.85	$119.90
Purchase #7	$182.83	7.125%	$195.8566	$195.86	$195.85	$195.90
7 purchase totals =	$822.21		$904.6947	$904.69	$904.70	$904.80