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	$189.33	6.422%	$201.4888	$201.49	$201.50	$201.50
Purchase #2	$42.44	11.844%	$47.4666	$47.47	$47.45	$47.50
Purchase #3	$235.44	9.795%	$258.5013	$258.50	$258.50	$258.50
Purchase #4	$247.32	9.762%	$271.4634	$271.46	$271.45	$271.50
Purchase #5	$215.30	5.762%	$227.7056	$227.71	$227.70	$227.70
Purchase #6	$72.87	12.871%	$82.2491	$82.25	$82.25	$82.20
Purchase #7	$56.37	8.611%	$61.224	$61.22	$61.20	$61.20
7 purchase totals =	$1,059.07		$1,150.0988	$1,150.10	$1,150.05	$1,150.10