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	$23.42	13.746%	$26.6393	$26.64	$26.65	$26.60
Purchase #2	$43.36	7.565%	$46.6402	$46.64	$46.65	$46.60
Purchase #3	$47.87	6.213%	$50.8442	$50.84	$50.85	$50.80
Purchase #4	$228.26	8.818%	$248.388	$248.39	$248.40	$248.40
Purchase #5	$246.52	13.871%	$280.7148	$280.71	$280.70	$280.70
Purchase #6	$60.59	13.645%	$68.8575	$68.86	$68.85	$68.90
Purchase #7	$55.38	13.325%	$62.7594	$62.76	$62.75	$62.80
7 purchase totals =	$705.40		$784.8434	$784.84	$784.85	$784.80