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	$177.87	7.666%	$191.5055	$191.51	$191.50	$191.50
Purchase #2	$164.63	4.344%	$171.7815	$171.78	$171.80	$171.80
Purchase #3	$248.84	4.259%	$259.4381	$259.44	$259.45	$259.40
Purchase #4	$237.39	5.106%	$249.5111	$249.51	$249.50	$249.50
Purchase #5	$28.43	12.817%	$32.0739	$32.07	$32.05	$32.10
Purchase #6	$168.39	7.808%	$181.5379	$181.54	$181.55	$181.50
Purchase #7	$70.57	11.813%	$78.9064	$78.91	$78.90	$78.90
7 purchase totals =	$1,096.12		$1,164.7544	$1,164.76	$1,164.75	$1,164.70