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	$249.56	12.575%	$280.9422	$280.94	$280.95	$280.90
Purchase #2	$141.67	11.802%	$158.3899	$158.39	$158.40	$158.40
Purchase #3	$118.42	13.316%	$134.1888	$134.19	$134.20	$134.20
Purchase #4	$60.49	11.365%	$67.3647	$67.36	$67.35	$67.40
Purchase #5	$174.65	3.576%	$180.8955	$180.90	$180.90	$180.90
Purchase #6	$76.88	6.823%	$82.1255	$82.13	$82.15	$82.10
Purchase #7	$85.95	3.836%	$89.247	$89.25	$89.25	$89.20
7 purchase totals =	$907.62		$993.1536	$993.16	$993.20	$993.10