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	$74.59	12.666%	$84.0376	$84.04	$84.05	$84.00
Purchase #2	$183.59	3.167%	$189.4043	$189.40	$189.40	$189.40
Purchase #3	$144.84	3.791%	$150.3309	$150.33	$150.35	$150.30
Purchase #4	$250.51	13.514%	$284.3639	$284.36	$284.35	$284.40
Purchase #5	$162.42	3.814%	$168.6147	$168.61	$168.60	$168.60
Purchase #6	$47.74	6.464%	$50.8259	$50.83	$50.85	$50.80
Purchase #7	$53.83	3.775%	$55.8621	$55.86	$55.85	$55.90
7 purchase totals =	$917.52		$983.4394	$983.43	$983.45	$983.40