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	$160.42	6.287%	$170.5056	$170.51	$170.50	$170.50
Purchase #2	$221.72	13.241%	$251.0779	$251.08	$251.10	$251.10
Purchase #3	$68.27	4.750%	$71.5128	$71.51	$71.50	$71.50
Purchase #4	$29.46	7.639%	$31.7104	$31.71	$31.70	$31.70
Purchase #5	$197.80	13.458%	$224.4199	$224.42	$224.40	$224.40
Purchase #6	$61.31	3.221%	$63.2848	$63.28	$63.30	$63.30
Purchase #7	$78.96	13.874%	$89.9149	$89.91	$89.90	$89.90
7 purchase totals =	$817.94		$902.4263	$902.42	$902.40	$902.40