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	$126.65	3.565%	$131.1651	$131.17	$131.15	$131.20
Purchase #2	$129.30	9.741%	$141.8951	$141.90	$141.90	$141.90
Purchase #3	$5.65	6.286%	$6.0052	$6.01	$6.00	$6.00
Purchase #4	$194.56	10.715%	$215.4071	$215.41	$215.40	$215.40
Purchase #5	$183.39	12.264%	$205.8809	$205.88	$205.90	$205.90
Purchase #6	$74.64	5.555%	$78.7863	$78.79	$78.80	$78.80
Purchase #7	$57.86	3.481%	$59.8741	$59.87	$59.85	$59.90
7 purchase totals =	$772.05		$839.0138	$839.03	$839.00	$839.10