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	$25.59	7.584%	$27.5307	$27.53	$27.55	$27.50
Purchase #2	$155.46	6.804%	$166.0375	$166.04	$166.05	$166.00
Purchase #3	$39.84	6.737%	$42.524	$42.52	$42.50	$42.50
Purchase #4	$145.29	3.639%	$150.5771	$150.58	$150.60	$150.60
Purchase #5	$247.89	9.337%	$271.0355	$271.04	$271.05	$271.00
Purchase #6	$175.89	7.831%	$189.6639	$189.66	$189.65	$189.70
Purchase #7	$221.47	7.395%	$237.8477	$237.85	$237.85	$237.80
7 purchase totals =	$1,011.43		$1,085.2164	$1,085.22	$1,085.25	$1,085.10