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	$75.60	6.401%	$80.4392	$80.44	$80.45	$80.40
Purchase #2	$123.94	10.486%	$136.9363	$136.94	$136.95	$136.90
Purchase #3	$120.83	5.177%	$127.0854	$127.09	$127.10	$127.10
Purchase #4	$55.50	11.217%	$61.7254	$61.73	$61.75	$61.70
Purchase #5	$208.71	9.689%	$228.9319	$228.93	$228.95	$228.90
Purchase #6	$118.61	11.119%	$131.7982	$131.80	$131.80	$131.80
Purchase #7	$55.46	7.462%	$59.5984	$59.60	$59.60	$59.60
7 purchase totals =	$758.65		$826.5148	$826.53	$826.60	$826.40