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	$81.68	6.175%	$86.7237	$86.72	$86.70	$86.70
Purchase #2	$27.83	12.698%	$31.3639	$31.36	$31.35	$31.40
Purchase #3	$52.36	5.782%	$55.3875	$55.39	$55.40	$55.40
Purchase #4	$127.26	8.206%	$137.703	$137.70	$137.70	$137.70
Purchase #5	$78.48	5.121%	$82.499	$82.50	$82.50	$82.50
Purchase #6	$63.38	6.572%	$67.5453	$67.55	$67.55	$67.50
Purchase #7	$43.80	6.751%	$46.7569	$46.76	$46.75	$46.80
7 purchase totals =	$474.79		$507.9793	$507.98	$507.95	$508.00