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	$47.48	9.556%	$52.0172	$52.02	$52.00	$52.00
Purchase #2	$148.48	12.214%	$166.6153	$166.62	$166.60	$166.60
Purchase #3	$57.60	6.655%	$61.4333	$61.43	$61.45	$61.40
Purchase #4	$50.54	11.820%	$56.5138	$56.51	$56.50	$56.50
Purchase #5	$55.99	12.514%	$62.9966	$63.00	$63.00	$63.00
Purchase #6	$84.41	7.517%	$90.7551	$90.76	$90.75	$90.80
Purchase #7	$102.95	6.328%	$109.4647	$109.46	$109.45	$109.50
7 purchase totals =	$547.45		$599.7960	$599.80	$599.75	$599.80