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	$73.86	6.787%	$78.8729	$78.87	$78.85	$78.90
Purchase #2	$80.49	11.115%	$89.4365	$89.44	$89.45	$89.40
Purchase #3	$92.60	7.241%	$99.3052	$99.31	$99.30	$99.30
Purchase #4	$134.71	6.581%	$143.5753	$143.58	$143.60	$143.60
Purchase #5	$224.49	6.839%	$239.8429	$239.84	$239.85	$239.80
Purchase #6	$185.80	13.566%	$211.0056	$211.01	$211.00	$211.00
Purchase #7	$66.50	12.861%	$75.0526	$75.05	$75.05	$75.10
7 purchase totals =	$858.45		$937.0910	$937.10	$937.10	$937.10