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	$97.63	3.218%	$100.7717	$100.77	$100.75	$100.80
Purchase #2	$55.41	4.470%	$57.8868	$57.89	$57.90	$57.90
Purchase #3	$174.46	4.525%	$182.3543	$182.35	$182.35	$182.40
Purchase #4	$36.92	12.826%	$41.6554	$41.66	$41.65	$41.70
Purchase #5	$71.74	9.274%	$78.3932	$78.39	$78.40	$78.40
Purchase #6	$234.42	4.114%	$244.064	$244.06	$244.05	$244.10
Purchase #7	$247.55	13.489%	$280.942	$280.94	$280.95	$280.90
7 purchase totals =	$918.13		$986.0674	$986.06	$986.05	$986.20