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	$28.68	3.700%	$29.7412	$29.74	$29.75	$29.70
Purchase #2	$215.47	4.646%	$225.4807	$225.48	$225.50	$225.50
Purchase #3	$136.46	13.307%	$154.6187	$154.62	$154.60	$154.60
Purchase #4	$112.96	10.109%	$124.3791	$124.38	$124.40	$124.40
Purchase #5	$42.36	9.383%	$46.3346	$46.33	$46.35	$46.30
Purchase #6	$39.79	6.602%	$42.4169	$42.42	$42.40	$42.40
Purchase #7	$47.89	10.360%	$52.8514	$52.85	$52.85	$52.90
7 purchase totals =	$623.61		$675.8226	$675.82	$675.85	$675.80