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	$71.89	11.842%	$80.4032	$80.40	$80.40	$80.40
Purchase #2	$183.96	7.558%	$197.8637	$197.86	$197.85	$197.90
Purchase #3	$182.60	12.783%	$205.9418	$205.94	$205.95	$205.90
Purchase #4	$152.33	12.646%	$171.5937	$171.59	$171.60	$171.60
Purchase #5	$217.26	3.294%	$224.4165	$224.42	$224.40	$224.40
Purchase #6	$79.31	12.437%	$89.1738	$89.17	$89.15	$89.20
Purchase #7	$101.29	7.695%	$109.0843	$109.08	$109.10	$109.10
7 purchase totals =	$988.64		$1,078.4770	$1,078.46	$1,078.45	$1,078.50