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	$68.65	12.428%	$77.1818	$77.18	$77.20	$77.20
Purchase #2	$196.55	13.711%	$223.499	$223.50	$223.50	$223.50
Purchase #3	$38.32	4.292%	$39.9647	$39.96	$39.95	$40.00
Purchase #4	$100.70	3.605%	$104.3302	$104.33	$104.35	$104.30
Purchase #5	$47.81	11.742%	$53.4239	$53.42	$53.40	$53.40
Purchase #6	$191.69	3.433%	$198.2707	$198.27	$198.25	$198.30
Purchase #7	$248.92	12.700%	$280.5328	$280.53	$280.55	$280.50
7 purchase totals =	$892.64		$977.2031	$977.19	$977.20	$977.20