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	$185.56	6.754%	$198.0927	$198.09	$198.10	$198.10
Purchase #2	$119.92	11.324%	$133.4997	$133.50	$133.50	$133.50
Purchase #3	$67.58	7.292%	$72.5079	$72.51	$72.50	$72.50
Purchase #4	$150.58	11.216%	$167.4691	$167.47	$167.45	$167.50
Purchase #5	$239.59	7.486%	$257.5257	$257.53	$257.55	$257.50
Purchase #6	$71.94	9.374%	$78.6837	$78.68	$78.70	$78.70
Purchase #7	$247.73	13.222%	$280.4849	$280.48	$280.50	$280.50
7 purchase totals =	$1,082.90		$1,188.2637	$1,188.26	$1,188.30	$1,188.30