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	$50.55	3.586%	$52.3627	$52.36	$52.35	$52.40
Purchase #2	$153.62	8.315%	$166.3935	$166.39	$166.40	$166.40
Purchase #3	$147.50	7.326%	$158.3059	$158.31	$158.30	$158.30
Purchase #4	$42.38	12.392%	$47.6317	$47.63	$47.65	$47.60
Purchase #5	$50.93	9.621%	$55.83	$55.83	$55.85	$55.80
Purchase #6	$246.35	13.865%	$280.5064	$280.51	$280.50	$280.50
Purchase #7	$166.56	5.452%	$175.6409	$175.64	$175.65	$175.60
7 purchase totals =	$857.89		$936.6711	$936.67	$936.70	$936.60