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	$10.40	8.630%	$11.2975	$11.30	$11.30	$11.30
Purchase #2	$72.81	12.709%	$82.0634	$82.06	$82.05	$82.10
Purchase #3	$171.46	9.344%	$187.4812	$187.48	$187.50	$187.50
Purchase #4	$134.65	13.417%	$152.716	$152.72	$152.70	$152.70
Purchase #5	$37.26	3.455%	$38.5473	$38.55	$38.55	$38.50
Purchase #6	$73.44	3.294%	$75.8591	$75.86	$75.85	$75.90
Purchase #7	$38.37	11.640%	$42.8363	$42.84	$42.85	$42.80
7 purchase totals =	$538.39		$590.8008	$590.81	$590.80	$590.80